title: Submarine

text: A concealed military submarine is a real threat, and because of its stealth, can force an enemy navy to waste resources searching large areas of ocean and protecting ships against attack. This advantage was vividly demonstrated in the 1982 Falklands War when the British nuclear-powered submarine sank the Argentine cruiser . After the sinking the Argentine Navy recognized that they had no effective defense against submarine attack, and the Argentine surface fleet withdrew to port for the remainder of the war, though an Argentine submarine remained at sea.


title: Submarine

text: Although the majority of the world's submarines are military, there are some civilian submarines, which are used for tourism, exploration, oil and gas platform inspections, and pipeline surveys. Some are also used in illegal activities.


title: Submarine

text: The Submarine Voyage ride opened at Disneyland in 1959, but although it ran under water it was not a true submarine, as it ran on tracks and was open to the atmosphere. The first tourist submarine was , which went into service in 1964 at Expo64. By 1997 there were 45 tourist submarines operating around the world. Submarines with a crush depth in the range of are operated in several areas worldwide, typically with bottom depths around , with a carrying capacity of 50 to 100 passengers.


title: Submarine

text: In a typical operation a surface vessel carries passengers to an offshore operating area and loads them into the submarine. The submarine then visits underwater points of interest such as natural or artificial reef structures. To surface safely without danger of collision the location of the submarine is marked with an air release and movement to the surface is coordinated by an observer in a support craft.


title: Submarine

text: A recent development is the deployment of so-called narco-submarines by South American drug smugglers to evade law enforcement detection. Although they occasionally deploy true submarines, most are self-propelled semi-submersibles, where a portion of the craft remains above water at all times. In September 2011, Colombian authorities seized a 16-meter-long submersible that could hold a crew of 5, costing about $2 million. The vessel belonged to FARC rebels and had the capacity to carry at least 7 tonnes of drugs.


title: Submarine

text: All surface ships, as well as surfaced submarines, are in a positively buoyant condition, weighing less than the volume of water they would displace if fully submerged. To submerge hydrostatically, a ship must have negative buoyancy, either by increasing its own weight or decreasing its displacement of water. To control their displacement and weight, submarines have ballast tanks, which can hold varying amounts of water and air.


title: Submarine

text: For general submersion or surfacing, submarines use the main ballast tanks (MBTs), which are ambient pressure tanks, filled with water to submerge, or with air to surface. While submerged, MBTs generally remain flooded, which simplifies their design, and on many submarines these tanks are a section of the space between the light hull and the pressure hull. For more precise control of depth, submarines use smaller depth control tanks (DCTs)—also called hard tanks (due to their ability to withstand higher pressure), or trim tanks. These are variable buoyancy pressure vessels, a type of buoyancy control device. The amount of water in depth control tanks can be adjusted to hydrostatically change depth or to maintain a constant depth as outside conditions (mainly water density) change. Depth control tanks may be located either near the submarine's center of gravity, to minimise the effect on trim, or separated along the length of the hull so they can also be used to adjust static trim by transfer of water between them.


title: Submarine

text: When submerged, the water pressure on a submarine's hull can reach for steel submarines and up to for titanium submarines like , while interior pressure remains relatively unchanged. This difference results in hull compression, which decreases displacement. Water density also marginally increases with depth, as the salinity and pressure are higher. This change in density incompletely compensates for hull compression, so buoyancy decreases as depth increases. A submerged submarine is in an unstable equilibrium, having a tendency to either sink or float to the surface. Keeping a constant depth requires continual operation of either the depth control tanks or control surfaces.


title: Submarine

text: Submarines in a neutral buoyancy condition are not intrinsically trim-stable. To maintain desired longitudinal trim, submarines use forward and aft trim tanks. Pumps move water between the tanks, changing weight distribution and pitching the sub up or down. A similar system may be used to maintain transverse trim.


title: Submarine

text: The hydrostatic effect of variable ballast tanks is not the only way to control the submarine underwater. Hydrodynamic maneuvering is done by several control surfaces, collectively known as diving planes or hydroplanes, which can be moved to create hydrodynamic forces when a submarine moves longitudinally at sufficient speed. In the classic cruciform stern configuration, the horizontal stern planes serve the same purpose as the trim tanks, controlling the trim. Most submarines additionally have forward horizontal planes, normally placed on the bow until the 1960s but often on the sail on later designs, where they are closer to the center of gravity and can control depth with less effect on the trim.


title: Submarine

text: An obvious way to configure the control surfaces at the stern of a submarine is to use vertical planes to control yaw and horizontal planes to control pitch, which gives them the shape of a cross when seen from astern of the vessel. In this configuration, which long remained the dominant one, the horizontal planes are used to control the trim and depth and the vertical planes to control sideways maneuvers, like the rudder of a surface ship.


title: Submarine

text: Alternatively, the rear control surfaces can be combined into what has become known as an x-stern or an x-rudder. Although less intuitive, such a configuration has turned out to have several advantages over the traditional cruciform arrangement. First, it improves maneuverability, horizontally as well as vertically. Second, the control surfaces are less likely to get damaged when landing on, or departing from, the seabed as well as when mooring and unmooring alongside. Finally, it is safer in that one of the two diagonal lines can counteract the other with respect to vertical as well as horizontal motion if one of them accidentally gets stuck.


title: Submarine

text: The x-stern was first tried in practice in the early 1960s on the USS "Albacore", an experimental submarine of the US Navy. While the arrangement was found to be advantageous, it was nevertheless not used on US production submarines that followed due to the fact that it requires the use of a computer to manipulate the control surfaces to the desired effect. Instead, the first to use an x-stern in standard operations was the Swedish Navy with its "Sjöormen" class, the lead submarine of which was launched in 1967, before the "Albacore" had even finished her test runs. Since it turned out to work very well in practice, all subsequent classes of Swedish submarines ("Näcken", "Västergötland", "Gotland", and "Blekinge" class) have or will come with an x-rudder.


title: Submarine

text: The Kockums shipyard responsible for the design of the x-stern on Swedish submarines eventually exported it to Australia with the "Collins" class as well as to Japan with the "Sōryū" class. With the introduction of the type 212, the German and Italian Navies came to feature it as well. The US Navy with its "Columbia" class, the British Navy with its "Dreadnought" class, and the French Navy with its "Barracuda" class are all about to join the x-stern family. Hence, as judged by the situation in the early 2020s, the x-stern is about to become the dominant technology.


title: Submarine

text: When a submarine performs an emergency surfacing, all depth and trim control methods are used simultaneously, together with propelling the boat upwards. Such surfacing is very quick, so the sub may even partially jump out of the water, potentially damaging submarine systems.


title: Submarine

text: Modern submarines are cigar-shaped. This design, also used in very early submarines, is sometimes called a "teardrop hull". It reduces hydrodynamic drag when the sub is submerged, but decreases the sea-keeping capabilities and increases drag while surfaced. Since the limitations of the propulsion systems of early submarines forced them to operate surfaced most of the time, their hull designs were a compromise. Because of the slow submerged speeds of those subs, usually, well below 10 kt (18 km/h), the increased drag for underwater travel was acceptable. Late in World War II, when technology allowed faster and longer submerged operation and increased aircraft surveillance forced submarines to stay submerged, hull designs became teardrop shaped again to reduce drag and noise. was a unique research submarine that pioneered the American version of the teardrop hull form (sometimes referred to as an "Albacore hull") of modern submarines. On modern military submarines the outer hull is covered with a layer of sound-absorbing rubber, or anechoic plating, to reduce detection.


title: Submarine

text: The occupied pressure hulls of deep-diving submarines such as are spherical instead of cylindrical. This allows a more even distribution of stress and efficient use of materials to withstand external pressure as it gives the most internal volume for structural weight and is the most efficient shape to avoid buckling instability in compression. A frame is usually affixed to the outside of the pressure hull, providing attachment for ballast and trim systems, scientific instrumentation, battery packs, syntactic flotation foam, and lighting.


title: Submarine

text: A raised tower on top of a standard submarine accommodates the periscope and electronics masts, which can include radio, radar, electronic warfare, and other systems. It might also include a snorkel mast. In many early classes of submarines (see history), the control room, or "conn", was located inside this tower, which was known as the "conning tower". Since then, the conn has been located within the hull of the submarine, and the tower is now called the "sail" or "fin". The conn is distinct from the "bridge", a small open platform in the top of the sail, used for observation during surface operation.


title: Submarine

text: "Bathtubs" are related to conning towers but are used on smaller submarines. The bathtub is a metal cylinder surrounding the hatch that prevents waves from breaking directly into the cabin. It is needed because surfaced submarines have limited freeboard, that is, they lie low in the water. Bathtubs help prevent swamping the vessel.


title: Submarine

text: Modern submarines and submersibles usually have, as did the earliest models, a single hull. Large submarines generally have an additional hull or hull sections outside. This external hull, which actually forms the shape of submarine, is called the outer hull ("casing" in the Royal Navy) or light hull, as it does not have to withstand a pressure difference. Inside the outer hull there is a strong hull, or pressure hull, which withstands sea pressure and has normal atmospheric pressure inside.


title: Submarine

text: As early as World War I, it was realized that the optimal shape for withstanding pressure conflicted with the optimal shape for seakeeping and minimal drag at the surface, and construction difficulties further complicated the problem. This was solved either by a compromise shape, or by using two layered hulls: the internal strength hull for withstanding pressure, and an external fairing for hydrodynamic shape. Until the end of World War II, most submarines had an additional partial casing on the top, bow and stern, built of thinner metal, which was flooded when submerged. Germany went further with the Type XXI, a general predecessor of modern submarines, in which the pressure hull was fully enclosed inside the light hull, but optimized for submerged navigation, unlike earlier designs that were optimized for surface operation.


title: Submarine

text: After World War II, approaches split. The Soviet Union changed its designs, basing them on German developments. All post-World War II heavy Soviet and Russian submarines are built with a double hull structure. American and most other Western submarines switched to a primarily single-hull approach. They still have light hull sections in the bow and stern, which house main ballast tanks and provide a hydrodynamically optimized shape, but the main cylindrical hull section has only a single plating layer. Double hulls are being considered for future submarines in the United States to improve payload capacity, stealth and range.


title: Submarine

text: The pressure hull is generally constructed of thick high-strength steel with a complex structure and high strength reserve, and is separated by watertight bulkheads into several compartments. There are also examples of more than two hulls in a submarine, like the , which has two main pressure hulls and three smaller ones for control room, torpedoes and steering gear, with the missile launch system between the main hulls, all surrounded and supported by the outer light hydrodynamic hull. When submerged the pressure hull provides most of the buoyancy for the whole vessel.


title: Submarine

text: The dive depth cannot be increased easily. Simply making the hull thicker increases the structural weight and requires reduction of onboard equipment weight, and increasing the diameter requires a proportional increase in thickness for the same material and architecture, ultimately resulting in a pressure hull that does not have sufficient buoyancy to support its own weight, as in a bathyscaphe. This is acceptable for civilian research submersibles, but not military submarines, which need to carry a large equipment, crew, and weapons load to fulfill their function. Construction materials with greater specific strength and specific modulus are needed.


title: Submarine

text: WWI submarines had hulls of carbon steel, with a maximum depth. During WWII, high-strength alloyed steel was introduced, allowing depths. High-strength alloy steel remains the primary material for submarines today, with depths, which cannot be exceeded on a military submarine without design compromises. To exceed that limit, a few submarines were built with titanium hulls. Titanium alloys can be stronger than steel, lighter, and most importantly, have higher immersed specific strength and specific modulus. Titanium is also not ferromagnetic, important for stealth. Titanium submarines were built by the Soviet Union, which developed specialized high-strength alloys. It has produced several types of titanium submarines. Titanium alloys allow a major increase in depth, but other systems must be redesigned to cope, so test depth was limited to for the , the deepest-diving combat submarine. An may have successfully operated at , though continuous operation at such depths would produce excessive stress on many submarine systems. Titanium does not flex as readily as steel, and may become brittle after many dive cycles. Despite its benefits, the high cost of titanium construction led to the abandonment of titanium submarine construction as the Cold War ended. Deep-diving civilian submarines have used thick acrylic pressure hulls. Although the specific strength and specific modulus of acrylic are not very high, the density is only 1.18g/cm, so it is only very slightly denser than water, and the buoyancy penalty of increased thickness is correspondingly low.


title: Submarine

text: The deepest deep-submergence vehicle (DSV) to date is "Trieste". On 5 October 1959, "Trieste" departed San Diego for Guam aboard the freighter "Santa Maria" to participate in "Project Nekton", a series of very deep dives in the Mariana Trench. On 23 January 1960, "Trieste" reached the ocean floor in the Challenger Deep (the deepest southern part of the Mariana Trench), carrying Jacques Piccard (son of Auguste) and Lieutenant Don Walsh, USN. This was the first time a vessel, crewed or uncrewed, had reached the deepest point in the Earth's oceans. The onboard systems indicated a depth of , although this was later revised to and more accurate measurements made in 1995 have found the Challenger Deep slightly shallower, at .


title: Submarine

text: Building a pressure hull is difficult, as it must withstand pressures at its required diving depth. When the hull is perfectly round in cross-section, the pressure is evenly distributed, and causes only hull compression. If the shape is not perfect, the hull deflects more in some places and buckling instabity is the usual failure mode. Inevitable minor deviations are resisted by stiffener rings, but even a one-inch (25 mm) deviation from roundness results in over 30 percent decrease of maximal hydrostatic load and consequently dive depth. The hull must therefore be constructed with high precision. All hull parts must be welded without defects, and all joints are checked multiple times with different methods, contributing to the high cost of modern submarines. (For example, each attack submarine costs US$2.6 billion, over US$200,000 per ton of displacement.)


title: Submarine

text: The first submarines were propelled by humans. The first mechanically driven submarine was the 1863 French , which used compressed air for propulsion. Anaerobic propulsion was first employed by the Spanish "Ictineo II" in 1864, which used a solution of zinc, manganese dioxide, and potassium chlorate to generate sufficient heat to power a steam engine, while also providing oxygen for the crew. A similar system was not employed again until 1940 when the German Navy tested a hydrogen peroxide-based system, the Walter turbine, on the experimental V-80 submarine and later on the naval and type XVII submarines; the system was further developed for the British , completed in 1958.


title: Submarine

text: Until the advent of nuclear marine propulsion, most 20th-century submarines used electric motors and batteries for running underwater and combustion engines on the surface, and for battery recharging. Early submarines used gasoline (petrol) engines but this quickly gave way to kerosene (paraffin) and then diesel engines because of reduced flammability and, with diesel, improved fuel-efficiency and thus also greater range. A combination of diesel and electric propulsion became the norm.


title: Submarine

text: Initially, the combustion engine and the electric motor were in most cases connected to the same shaft so that both could directly drive the propeller. The combustion engine was placed at the front end of the stern section with the electric motor behind it followed by the propeller shaft. The engine was connected to the motor by a clutch and the motor in turn connected to the propeller shaft by another clutch.


title: Submarine

text: With only the rear clutch engaged, the electric motor could drive the propeller, as required for fully submerged operation. With both clutches engaged, the combustion engine could drive the propeller, as was possible when operating on the surface or, at a later stage, when snorkeling. The electric motor would in this case serve as a generator to charge the batteries or, if no charging was needed, be allowed to rotate freely. With only the front clutch engaged, the combustion engine could drive the electric motor as a generator for charging the batteries without simultaneously forcing the propeller to move.


title: Submarine

text: The motor could have multiple armatures on the shaft, which could be electrically coupled in series for slow speed and in parallel for high speed (these connections were called "group down" and "group up", respectively).


title: Submarine

text: While most early submarines used a direct mechanical connection between the combustion engine and the propeller, an alternative solution was considered as well as implemented at a very early stage. That solution consists in first converting the work of the combustion engine into electric energy via a dedicated generator. This energy is then used to drive the propeller via the electric motor and, to the extent required, for charging the batteries. In this configuration, the electric motor is thus responsible for driving the propeller at all times, regardless of whether air is available so that the combustion engine can also be used or not.


title: Submarine

text: Among the pioneers of this alternative solution was the very first submarine of the Swedish Navy, (later renamed "Ub no 1"), launched in 1904. While its design was generally inspired by the first submarine commissioned by the US Navy, USS "Holland", it deviated from the latter in at least three significant ways: by adding a periscope, by replacing the gasoline engine by a semidiesel engine (a hot-bulb engine primarily meant to be fueled by kerosene, later replaced by a true diesel engine) and by severing the mechanical link between the combustion engine and the propeller by instead letting the former drive a dedicated generator. By so doing, it took three significant steps toward what was eventually to become the dominant technology for conventional (i.e., non-nuclear) submarines.


title: Submarine

text: In the following years, the Swedish Navy added another seven submarines in three different classes (, , and ) using the same propulsion technology but fitted with true diesel engines rather than semidiesels from the outset. Since by that time, the technology was usually based on the diesel engine rather than some other type of combustion engine, it eventually came to be known as diesel–electric transmission.


title: Submarine

text: Like many other early submarines, those initially designed in Sweden were quite small (less than 200 tonnes) and thus confined to littoral operation. When the Swedish Navy wanted to add larger vessels, capable of operating further from the shore, their designs were purchased from companies abroad that already had the required experience: first Italian (Fiat-Laurenti) and later German (A.G. Weser and IvS). As a side-effect, the diesel–electric transmission was temporarily abandoned.


title: Submarine

text: However, diesel–electric transmission was immediately reintroduced when Sweden began designing its own submarines again in the mid 1930s. From that point onwards, it has been consistently used for all new classes of Swedish submarines, albeit supplemented by air-independent propulsion (AIP) as provided by Stirling engines beginning with HMS "Näcken" in 1988.


title: Submarine

text: Another early adopter of diesel–electric transmission was the US Navy, whose Bureau of Engineering proposed its use in 1928. It was subsequently tried in the S-class submarines , , and before being put into production with the "Porpoise" class of the 1930s. From that point onwards, it continued to be used on most US conventional submarines.


title: Submarine

text: Apart from the British U-class and some submarines of the Imperial Japanese Navy that used separate diesel generators for low speed running, few navies other than those of Sweden and the US made much use of diesel–electric transmission before 1945. After World War II, by contrast, it gradually became the dominant mode of propulsion for conventional submarines. However, its adoption was not always swift. Notably, the Soviet Navy did not introduce diesel–electric transmission on its conventional submarines until 1980 with its "Paltus" class.


title: Submarine

text: If diesel–electric transmission had only brought advantages and no disadvantages in comparison with a system that mechanically connects the diesel engine to the propeller, it would undoubtedly have become dominant much earlier. The disadvantages include the following:


title: Submarine

text: The reason why diesel–electric transmission has become the dominant alternative in spite of these disadvantages is of course that it also comes with many advantages and that, on balance, these have eventually been found to be more important. The advantages include the following:


title: Submarine

text: During World War II the Germans experimented with the idea of the "schnorchel" (snorkel) from captured Dutch submarines but did not see the need for them until rather late in the war. The "schnorchel" is a retractable pipe that supplies air to the diesel engines while submerged at periscope depth, allowing the boat to cruise and recharge its batteries while maintaining a degree of stealth.


title: Submarine

text: Especially as first implemented however, it turned out to be far from a perfect solution. There were problems with the device's valve sticking shut or closing as it dunked in rough weather. Since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, and the crew often suffered painful ear injuries. Speed was limited to , lest the device snap from stress. The "schnorchel" also created noise that made the boat easier to detect with sonar, yet more difficult for the on-board sonar to detect signals from other vessels. Finally, allied radar eventually became sufficiently advanced that the "schnorchel" mast could be detected beyond visual range.


title: Submarine

text: While the snorkel renders a submarine far less detectable, it is thus not perfect. In clear weather, diesel exhausts can be seen on the surface to a distance of about three miles, while "periscope feather" (the wave created by the snorkel or periscope moving through the water) is visible from far off in calm sea conditions. Modern radar is also capable of detecting a snorkel in calm sea conditions.


title: Submarine

text: The problem of the diesels causing a vacuum in the submarine when the head valve is submerged still exists in later model diesel submarines but is mitigated by high-vacuum cut-off sensors that shut down the engines when the vacuum in the ship reaches a pre-set point. Modern snorkel induction masts have a fail-safe design using compressed air, controlled by a simple electrical circuit, to hold the "head valve" open against the pull of a powerful spring. Seawater washing over the mast shorts out exposed electrodes on top, breaking the control, and shutting the "head valve" while it is submerged. US submarines did not adopt the use of snorkels until after WWII.


title: Submarine

text: During World War II, German Type XXI submarines (also known as ""Elektroboote"") were the first submarines designed to operate submerged for extended periods. Initially they were to carry hydrogen peroxide for long-term, fast air-independent propulsion, but were ultimately built with very large batteries instead. At the end of the War, the British and Soviets experimented with hydrogen peroxide/kerosene (paraffin) engines that could run surfaced and submerged. The results were not encouraging. Though the Soviet Union deployed a class of submarines with this engine type (codenamed by NATO), they were considered unsuccessful.


title: Submarine

text: The United States also used hydrogen peroxide in an experimental midget submarine, X-1. It was originally powered by a hydrogen peroxide/diesel engine and battery system until an explosion of her hydrogen peroxide supply on 20 May 1957. X-1 was later converted to use diesel–electric drive.


title: Submarine

text: Today several navies use air-independent propulsion. Notably Sweden uses Stirling technology on the and s. The Stirling engine is heated by burning diesel fuel with liquid oxygen from cryogenic tanks. A newer development in air-independent propulsion is hydrogen fuel cells, first used on the German Type 212 submarine, with nine 34 kW or two 120 kW cells. Fuel cells are also used in the new Spanish s although with the fuel stored as ethanol and then converted into hydrogen before use.


title: Submarine

text: One new technology that is being introduced starting with the Japanese Navy's eleventh "Sōryū"-class submarine (JS "Ōryū") is a more modern battery, the lithium-ion battery. These batteries have about double the electric storage of traditional batteries, and by changing out the lead-acid batteries in their normal storage areas plus filling up the large hull space normally devoted to AIP engine and fuel tanks with many tons of lithium-ion batteries, modern submarines can actually return to a "pure" diesel–electric configuration yet have the added underwater range and power normally associated with AIP equipped submarines.


title: Submarine

text: Steam power was resurrected in the 1950s with a nuclear-powered steam turbine driving a generator. By eliminating the need for atmospheric oxygen, the time that a submarine could remain submerged was limited only by its food stores, as breathing air was recycled and fresh water distilled from seawater. More importantly, a nuclear submarine has unlimited range at top speed. This allows it to travel from its operating base to the combat zone in a much shorter time and makes it a far more difficult target for most anti-submarine weapons. Nuclear-powered submarines have a relatively small battery and diesel engine/generator powerplant for emergency use if the reactors must be shut down.


title: Submarine

text: Nuclear power is now used in all large submarines, but due to the high cost and large size of nuclear reactors, smaller submarines still use diesel–electric propulsion. The ratio of larger to smaller submarines depends on strategic needs. The US Navy, French Navy, and the British Royal Navy operate only nuclear submarines, which is explained by the need for distant operations. Other major operators rely on a mix of nuclear submarines for strategic purposes and diesel–electric submarines for defense. Most fleets have no nuclear submarines, due to the limited availability of nuclear power and submarine technology.


title: Submarine

text: Diesel–electric submarines have a stealth advantage over their nuclear counterparts. Nuclear submarines generate noise from coolant pumps and turbo-machinery needed to operate the reactor, even at low power levels. Some nuclear submarines such as the American can operate with their reactor coolant pumps secured, making them quieter than electric subs. A conventional submarine operating on batteries is almost completely silent, the only noise coming from the shaft bearings, propeller, and flow noise around the hull, all of which stops when the sub hovers in mid-water to listen, leaving only the noise from crew activity. Commercial submarines usually rely only on batteries, since they operate in conjunction with a mother ship.


title: Submarine

text: Several serious nuclear and radiation accidents have involved nuclear submarine mishaps. The reactor accident in 1961 resulted in 8 deaths and more than 30 other people were over-exposed to radiation. The reactor accident in 1968 resulted in 9 fatalities and 83 other injuries. The accident in 1985 resulted in 10 fatalities and 49 other radiation injuries.


title: Submarine

text: Oil-fired steam turbines powered the British K-class submarines, built during World War I and later, to give them the surface speed to keep up with the battle fleet. The K-class subs were not very successful, however.


title: Submarine

text: Toward the end of the 20th century, some submarines—such as the British "Vanguard" class—began to be fitted with pump-jet propulsors instead of propellers. Though these are heavier, more expensive, and less efficient than a propeller, they are significantly quieter, providing an important tactical advantage.


title: Submarine

text: The success of the submarine is inextricably linked to the development of the torpedo, invented by Robert Whitehead in 1866. His invention is essentially the same now as it was 140 years ago. Only with self-propelled torpedoes could the submarine make the leap from novelty to a weapon of war. Until the perfection of the guided torpedo, multiple "straight-running" torpedoes were required to attack a target. With at most 20 to 25 torpedoes stored on board, the number of attacks was limited. To increase combat endurance most World War I submarines functioned as submersible gunboats, using their deck guns against unarmed targets, and diving to escape and engage enemy warships. The importance of guns encouraged the development of the unsuccessful Submarine Cruiser such as the French and the Royal Navy's and M-class submarines. With the arrival of anti-submarine warfare (ASW) aircraft, guns became more for defense than attack. A more practical method of increasing combat endurance was the external torpedo tube, loaded only in port.


title: Submarine

text: The ability of submarines to approach enemy harbours covertly led to their use as minelayers. Minelaying submarines of World War I and World War II were specially built for that purpose. Modern submarine-laid mines, such as the British Mark 5 Stonefish and Mark 6 Sea Urchin, can be deployed from a submarine's torpedo tubes.


title: Submarine

text: After World War II, both the US and the USSR experimented with submarine-launched cruise missiles such as the SSM-N-8 Regulus and P-5 Pyatyorka. Such missiles required the submarine to surface to fire its missiles. They were the forerunners of modern submarine-launched cruise missiles, which can be fired from the torpedo tubes of submerged submarines, for example, the US BGM-109 Tomahawk and Russian RPK-2 Viyuga and versions of surface-to-surface anti-ship missiles such as the Exocet and Harpoon, encapsulated for submarine launch. Ballistic missiles can also be fired from a submarine's torpedo tubes, for example, missiles such as the anti-submarine SUBROC. With internal volume as limited as ever and the desire to carry heavier warloads, the idea of the external launch tube was revived, usually for encapsulated missiles, with such tubes being placed between the internal pressure and outer streamlined hulls.


title: Submarine

text: The strategic mission of the SSM-N-8 and the P-5 was taken up by submarine-launched ballistic missile beginning with the US Navy's Polaris missile, and subsequently the Poseidon and Trident missiles.


title: Submarine

text: Germany is working on the torpedo tube-launched short-range IDAS missile, which can be used against ASW helicopters, as well as surface ships and coastal targets.


title: Submarine

text: A submarine can have a variety of sensors, depending on its missions. Modern military submarines rely almost entirely on a suite of passive and active sonars to locate targets. Active sonar relies on an audible "ping" to generate echoes to reveal objects around the submarine. Active systems are rarely used, as doing so reveals the sub's presence. Passive sonar is a set of sensitive hydrophones set into the hull or trailed in a towed array, normally trailing several hundred feet behind the sub. The towed array is the mainstay of NATO submarine detection systems, as it reduces the flow noise heard by operators. Hull mounted sonar is employed in addition to the towed array, as the towed array can't work in shallow depth and during maneuvering. In addition, sonar has a blind spot "through" the submarine, so a system on both the front and back works to eliminate that problem. As the towed array trails behind and below the submarine, it also allows the submarine to have a system both above and below the thermocline at the proper depth; sound passing through the thermocline is distorted resulting in a lower detection range.


title: Submarine

text: Submarines also carry radar equipment to detect surface ships and aircraft. Submarine captains are more likely to use radar detection gear than active radar to detect targets, as radar can be detected far beyond its own return range, revealing the submarine. Periscopes are rarely used, except for position fixes and to verify a contact's identity.


title: Submarine

text: Civilian submarines, such as the or the Russian "Mir" submersibles, rely on small active sonar sets and viewing ports to navigate. The human eye cannot detect sunlight below about underwater, so high intensity lights are used to illuminate the viewing area.


title: Submarine

text: Early submarines had few navigation aids, but modern subs have a variety of navigation systems. Modern military submarines use an inertial guidance system for navigation while submerged, but drift error unavoidably builds over time. To counter this, the crew occasionally uses the Global Positioning System to obtain an accurate position. The periscope—a retractable tube with a prism system that provides a view of the surface—is only used occasionally in modern submarines, since the visibility range is short. The and s use photonics masts rather than hull-penetrating optical periscopes. These masts must still be deployed above the surface, and use electronic sensors for visible light, infrared, laser range-finding, and electromagnetic surveillance. One benefit to hoisting the mast above the surface is that while the mast is above the water the entire sub is still below the water and is much harder to detect visually or by radar.


title: Submarine

text: Military submarines use several systems to communicate with distant command centers or other ships. One is VLF (very low frequency) radio, which can reach a submarine either on the surface or submerged to a fairly shallow depth, usually less than . ELF (extremely low frequency) can reach a submarine at greater depths, but has a very low bandwidth and is generally used to call a submerged sub to a shallower depth where VLF signals can reach. A submarine also has the option of floating a long, buoyant wire antenna to a shallower depth, allowing VLF transmissions by a deeply submerged boat.


title: Submarine

text: By extending a radio mast, a submarine can also use a "burst transmission" technique. A burst transmission takes only a fraction of a second, minimizing a submarine's risk of detection.


title: Submarine

text: To communicate with other submarines, a system known as Gertrude is used. Gertrude is basically a sonar telephone. Voice communication from one submarine is transmitted by low power speakers into the water, where it is detected by passive sonars on the receiving submarine. The range of this system is probably very short, and using it radiates sound into the water, which can be heard by the enemy.


title: Submarine

text: Civilian submarines can use similar, albeit less powerful systems to communicate with support ships or other submersibles in the area.


title: Submarine

text: With nuclear power or air-independent propulsion, submarines can remain submerged for months at a time. Conventional diesel submarines must periodically resurface or run on snorkel to recharge their batteries. Most modern military submarines generate breathing oxygen by electrolysis of fresh water (using a device called an "Electrolytic Oxygen Generator"). Emergency oxygen can be produced by burning sodium chlorate candles. Atmosphere control equipment includes a Carbon dioxide scrubber, which uses a spray of monoethanolamine (MEA) absorbent to remove the gas from the air, after which the MEA is heated in a boiler to release the CO which is then pumped overboard. Emergency scrubbing can also be done with lithium hydroxide, which is consumable. A machine that uses a catalyst to convert carbon monoxide into carbon dioxide (removed by the scrubber) and bonds hydrogen produced from the ship's storage battery with oxygen in the atmosphere to produce water, is also used. An atmosphere monitoring system samples the air from different areas of the ship for nitrogen, oxygen, hydrogen, R-12 and R-114 refrigerants, carbon dioxide, carbon monoxide, and other gases. Poisonous gases are removed, and oxygen is replenished by use of an oxygen bank located in a main ballast tank. Some heavier submarines have two oxygen bleed stations (forward and aft). The oxygen in the air is sometimes kept a few percent less than atmospheric concentration to reduce fire risk.


title: Submarine

text: Fresh water is produced by either an evaporator or a reverse osmosis unit. The primary use for fresh water is to provide feedwater for the reactor and steam propulsion plants. It is also available for showers, sinks, cooking and cleaning once propulsion plant needs have been met. Seawater is used to flush toilets, and the resulting "blackwater" is stored in a sanitary tank until it is blown overboard using pressurized air or pumped overboard by using a special sanitary pump. The blackwater-discharge system requires skill to operate, and isolation valves must be closed before discharge. The German Type VIIC boat was lost with casualties because of human error while using this system. Water from showers and sinks is stored separately in "grey water" tanks and discharged overboard using drain pumps.


title: Submarine

text: Trash on modern large submarines is usually disposed of using a tube called a Trash Disposal Unit (TDU), where it is compacted into a galvanized steel can. At the bottom of the TDU is a large ball valve. An ice plug is set on top of the ball valve to protect it, the cans atop the ice plug. The top breech door is shut, and the TDU is flooded and equalized with sea pressure, the ball valve is opened and the cans fall out assisted by scrap iron weights in the cans. The TDU is also flushed with seawater to ensure it is completely empty and the ball valve is clear before closing the valve.


title: Submarine

text: A typical nuclear submarine has a crew of over 80; conventional boats typically have fewer than 40. The conditions on a submarine can be difficult because crew members must work in isolation for long periods of time, without family contact, and in cramped conditions. Submarines normally maintain radio silence to avoid detection. Operating a submarine is dangerous, even in peacetime, and many submarines have been lost in accidents.


title: Submarine

text: Most navies prohibited women from serving on submarines, even after they had been permitted to serve on surface warships. The Royal Norwegian Navy became the first navy to allow women on its submarine crews in 1985. The Royal Danish Navy allowed female submariners in 1988. Others followed suit including the Swedish Navy (1989), the Royal Australian Navy (1998), the Spanish Navy (1999), the German Navy (2001) and the Canadian Navy (2002). In 1995, Solveig Krey of the Royal Norwegian Navy became the first female officer to assume command on a military submarine, HNoMS "Kobben".


title: Submarine

text: On 8 December 2011, British Defence Secretary Philip Hammond announced that the UK's ban on women in submarines was to be lifted from 2013. Previously there were fears that women were more at risk from a build-up of carbon dioxide in the submarine. But a study showed no medical reason to exclude women, though pregnant women would still be excluded. Similar dangers to the pregnant woman and her fetus barred women from submarine service in Sweden in 1983, when all other positions were made available for them in the Swedish Navy. Today, pregnant women are still not allowed to serve on submarines in Sweden. However, the policymakers thought that it was discriminatory with a general ban and demanded that women should be tried on their individual merits and have their suitability evaluated and compared to other candidates. Further, they noted that a woman complying with such high demands is unlikely to become pregnant. In May 2014, three women became the RN's first female submariners.


title: Submarine

text: Women have served on US Navy surface ships since 1993, and , began serving on submarines for the first time. Until presently, the Navy allowed only three exceptions to women being on board military submarines: female civilian technicians for a few days at most, women midshipmen on an overnight during summer training for Navy ROTC and Naval Academy, and family members for one-day dependent cruises. In 2009, senior officials, including then-Secretary of the Navy Ray Mabus, Joint Chief of Staff Admiral Michael Mullen, and Chief of Naval Operations Admiral Gary Roughead, began the process of finding a way to implement women on submarines. The US Navy rescinded its "no women on subs" policy in 2010.


title: Submarine

text: Both the US and British navies operate nuclear-powered submarines that deploy for periods of six months or longer. Other navies that permit women to serve on submarines operate conventionally powered submarines, which deploy for much shorter periods—usually only for a few months. Prior to the change by the US, no nation using nuclear submarines permitted women to serve on board.


title: Submarine

text: In 2011, the first class of female submarine officers graduated from Naval Submarine School's Submarine Officer Basic Course (SOBC) at the Naval Submarine Base New London. Additionally, more senior ranking and experienced female supply officers from the surface warfare specialty attended SOBC as well, proceeding to fleet Ballistic Missile (SSBN) and Guided Missile (SSGN) submarines along with the new female submarine line officers beginning in late 2011. By late 2011, several women were assigned to the "Ohio"-class ballistic missile submarine . On 15 October 2013, the US Navy announced that two of the smaller "Virginia"-class attack submarines, and , would have female crew-members by January 2015.


title: Submarine

text: In an emergency, submarines can transmit a signal to other ships. The crew can use escape sets such as the Submarine Escape Immersion Equipment to abandon the submarine via an escape trunk, which is a small airlock compartment that provides a route for crew to escape from a downed submarine at ambient pressure in small groups, while minimising the amount of water admitted to the submarine. The crew can avoid lung injury from over-expansion of air in the lungs due to the pressure change known as pulmonary barotrauma by maintaining an open airway and exhaling during the ascent. Following escape from a pressurized submarine, in which the air pressure is higher than atmospheric due to water ingress or other reasons, the crew is at risk of developing decompression sickness on return to surface pressure.


title: Submarine

text: An alternative escape means is via a deep-submergence rescue vehicle that can dock onto the disabled submarine, establish a seal around the escape hatch, and transfer personnel at the same pressure as the interior of the submarine. If the submarine has been pressurised the survivors can lock into a decompression chamber on the submarine rescue ship and transfer under pressure for safe surface decompression.


title: Tati Gabrielle

text: Tatiana Gabrielle Hobson (born January 25, 1996) is an American actress. She is known for her roles as Gaia on The CW science fiction television series "The 100", Prudence on the Netflix original series "Chilling Adventures of Sabrina", Marienne Bellamy on the Netflix series" You", and for providing the voice of Willow Park on the Disney animated series "The Owl House". She played Jo Braddock, the lead villain, in the 2022 movie "Uncharted".


title: Tati Gabrielle

text: Hobson was born on January 25, 1996, in San Francisco, California. She is one of three children born to mother Traci Hewwit Hobson, who is of Korean and African American descent and raised by her adoptive Black family, and African American father Terry Hobson. She began acting in the third grade, in an adaptation of Lemony Snicket's "A Series of Unfortunate Events", where she played the main role of Lemony Snicket. She auditioned for Oakland School for the Arts in middle school and was accepted into their theatre program. She has performed in and directed several productions and has won multiple awards for her work at various theatre festivals, including the Edinburgh Festival Fringe in Scotland.


title: Tati Gabrielle

text: Hobson graduated from Oakland School for the Arts with a 3.7 GPA. She moved to Atlanta after high school to attend Spelman College, where she majored in Drama and French.


title: Tati Gabrielle

text: As Tatiana Hobson, Gabrielle's first credit is for her role as Keating in the 2014 short film "To Stay the Sword". In 2015, Gabrielle moved to Los Angeles. She starred in the 2015 short film "Tatterdemalion" and the 2016 television film "Just Jenna" as Monique.


title: Tati Gabrielle

text: Her first credit as Tati Gabrielle came in 2016 for her guest role as Wackie Jackie in the "Tightrope of Doom" episode of the Disney Channel comedy series "K.C. Undercover". Later that year, Gabrielle also starred in Nickelodeon's "The Thundermans" in the episode "Stealing Home" as Hacksaw.


title: Tati Gabrielle

text: In 2017, Gabrielle landed her first recurring role as Gaia in The CW apocalyptic drama "The 100". That same year, she was featured in an episode titled "Bob" of the Hulu anthology series "Dimension 404", where she portrayed Amanda's sister. Gabrielle also voiced Addie in the 2017 film "The Emoji Movie", her first major film role, and recurred in the second season of Hulu's "Freakish" as Birdie and on the TBS animated series "Tarantula".


title: Tati Gabrielle

text: In March 2018, Gabrielle was cast as a series regular in the role of Prudence in the Netflix original series, "Chilling Adventures of Sabrina". In 2020, Gabrielle was cast in a main role as Marienne Bellamy on the third season of the Netflix psychological thriller series "You", and continues to be so on the fourth season. In 2022, Gabrielle starred as the villain Jo Braddock in the film "Uncharted".


title: Mos Def

text: Yasiin Bey (; born Dante Terrell Smith, December 11, 1973), previously and more commonly known by his stage name Mos Def (), is an American rapper, singer, songwriter, and actor. His hip hop career began in 1994, alongside his siblings in the short-lived rap group Urban Thermo Dynamics (UTD), after which they appeared on albums by Da Bush Babees and De La Soul. He formed the duo Black Star, alongside fellow Brooklyn-based rapper Talib Kweli, and in 1998 they released their debut album "Mos Def & Talib Kweli Are Black Star", featuring the singles "Definition" and "Respiration". He was featured on the roster of Rawkus Records and in 1999 released his solo debut, "Black on Both Sides". His debut was followed by "The New Danger" (2004), "True Magic" (2006), and "The Ecstatic" (2009). About.com listed him 14th on its "50 Greatest Rappers of All Time". His hits include "Oh No", "Ms. Fat Booty", and "Mathematics".


title: Mos Def

text: He was a child actor in television films, sitcoms, and theater. Since the early 2000s, he has appeared in the films "Something the Lord Made", "Next Day Air", "The Hitchhiker's Guide to the Galaxy", "16 Blocks", "Be Kind Rewind", "The Italian Job", "The Woodsman", "Bamboozled", and "Brown Sugar" and in television series such as "Dexter" and "House". He hosted "Def Poetry Jam" from 2002 to 2007.


title: Mos Def

text: Bey has been vocal on several social and political causes, including police brutality, American exceptionalism, and the status of African Americans.


title: Mos Def

text: Yasiin Bey was born Dante Terrell Smith on December 11, 1973, in Brooklyn, New York City, the son of Sheron Smith and Abdulrahman Smith. The eldest of 12 children and step-children, he was raised by his mother in Brooklyn, while his father lived in New Jersey.


title: Mos Def

text: His father was initially a member of the Nation of Islam and later followed Imam Warith Deen Mohammed, who merged into the mainstream Sunni Islam from the Nation of Islam. Bey was not exposed to Islam until the age of 13. He is close friends with fellow Muslim hip-hop artists Ali Shaheed Muhammad and Q-Tip.


title: Mos Def

text: Bey attended middle school at Philippa Schuyler Middle School in Bushwick, Brooklyn, where developed his love for acting. After returning from filming "You Take the Kids" in Los Angeles, and getting into a relationship with an older girl, Bey dropped out of high school during sophomore year. Growing up in New York City, during the crack epidemic of the 1980s and early 1990s, he has spoken about witnessing widespread instances of gang violence, theft, and poverty in society, which he largely avoided by working on plays, Off-Off-Broadway and arts programs. In a particularly traumatic childhood experience, Bey witnessed his then five-year-old younger brother, Ilias Bey (born Denard Smith), get hit by a car. Ilias later adopted the alias DCQ and was described by Bey as "my first partner in hip hop".


title: Mos Def

text: Bey began his music career in 1994, forming the group UTD (or Urban Thermo Dynamics) along with younger brother DCQ and high-school friend Ces. In 2004, they released the album "Manifest Destiny", their first and only release to date. The album features a compilation of previously unreleased and re-released tracks recorded during the original UTD run.


title: Mos Def

text: In 1996, Bey emerged as a solo artist and worked with De La Soul and Da Bush Babees, before he released his own first single, "Universal Magnetic" in 1997.


title: Mos Def

text: Bey signed with Rawkus Records and formed the rap group Black Star with Talib Kweli. The duo released an album, "Mos Def & Talib Kweli Are Black Star", in 1998. Mostly produced by Hi-Tek, the album featured the singles "Respiration" and "Definition", which both reached in the Billboard Hot R&B/Hip-Hop Songs chart.


title: Mos Def

text: Bey released his solo debut album "Black on Both Sides" in October 1999, also through Rawkus. The single "Ms. Fat Booty" charted, while the album reached #25 on the Billboard 200. Around this time, he also contributed to the Scritti Politti album "Anomie & Bonhomie".


title: Mos Def

text: In January 2002, Rawkus Records was taken over by Geffen Records, which released his second solo album "The New Danger" in October 2004. It included contributions by Shuggie Otis and Bernie Worrell, Doug Wimbish, and Will Calhoun as the Black Jack Johnson Band. The album reached #5 on the Billboard 200, making it the most successful for the artist to date. The single "Sex, Love & Money" charted, and was nominated for a Grammy Award. Mos Def's final solo album for Geffen Records, titled "True Magic", was released in 2006.


title: Mos Def

text: On November 7, 2007, Bey performed live in San Francisco at The Mezzanine venue. The performance was recorded for an upcoming "Live in Concert" DVD. During the event, he announced that he would be releasing a new album to be called "The Ecstatic". He performed a number of new tracks; in later shows, he previewed tracks produced by Madlib and was rumored to be going to Kanye West for new material. Producer and fellow Def Poet Al Be Back revealed he would be producing on the album as well. The album was released on June 9, 2009; but only Madlib's production had made the cut, along with tracks by Preservation, The Neptunes, Mr. Flash, Madlib's brother Oh No, J. Dilla, and Georgia Anne Muldrow.


title: Mos Def

text: Bey appears alongside Kanye West on the track "Two Words" from "The College Dropout" album, the track "Drunk and Hot Girls" and the bonus track "Good Night" off West's third major album, "Graduation". In 2002, he released the 12" single "Fine", which was featured in the "Brown Sugar" Motion Picture Soundtrack.


title: Mos Def

text: Bey also appears on the debut album from fellow New Yorkers Apollo Heights on a track titled, "Concern". In October, he signed a deal with Downtown Records and appeared on a remix to the song "D.A.N.C.E". by Justice. He appeared on Stephen Marley's debut album "Mind Control" on the song "Hey Baby". In 2009, he worked with Somali-Canadian rapper K'naan to produce the track "America" for K'naan's album "Troubadour".


title: Mos Def

text: In April 2008, he appeared on the title track for a new album by The Roots titled "Rising Down". The new single, "Life In Marvelous Times", was made officially available through iTunes on November 4, 2008, and was also available for stream on the Roots' website Okayplayer.


title: Mos Def

text: In April 2009, Bey traveled to South Africa for the first time, and performed with The Robert Glasper Experiment at the renowned Cape Town International Jazz Festival. He treated the South African audience with an encore, introduced by his own rendition of John Coltrane's "A Love Supreme", followed by a sneak preview of the track "M.D. (Doctor)".


title: Mos Def

text: Bey has designed two pairs of limited edition Converse shoes. The shoes were released through Foot Locker stores on August 1, 2009 in limited amounts.


title: Mos Def

text: In late 2009, he created his own clothing line with the "UNDRCRWN" brand called the "Mos Def Cut & Sew Collection". The items were released in select U.S. stores and almost exclusively on the UNDRCRWN website. That year, he was among the MCs aligned with American entrepreneur Damon Dash's DD172 and collaborating with American blues rock band the Black Keys on the "Blakroc" album, a project headed by the Black Keys and Damon Dash. Bey appeared with Harlem-bred rapper Jim Jones and the Black Keys on the Late Show with David Letterman to perform the "Blakroc" track "Ain't Nothing Like You (Hoochie Coo)".


title: Mos Def

text: In March 2010, Bey's song "Quiet Dog Bite Hard" was featured in Palm's "Life moves fast. Don't miss a thing." campaign.


title: Mos Def

text: Bey features on the first single, "Stylo", from the third Gorillaz album, "Plastic Beach", alongside soul legend Bobby Womack. He also appears on the track titled "Sweepstakes".


title: Mos Def

text: In September 2010, after appearing on Kanye West's G.O.O.D. Friday track "Lord Lord Lord", Bey confirmed he had signed with GOOD Music. Bey has been an active contributor to the recovery of the oil spill in the Gulf, performing concerts and raising money towards repairing its damages. In June 2010, he recorded a cover of the classic New Orleans song originally by Smokey Johnson, "It Ain't My Fault" with the Preservation Hall Jazz Band, Lenny Kravitz and Trombone Shorty.


title: Mos Def

text: In September 2011, the rapper announced that he legally changed his name to Yasiin Bey and would go by that name, retiring his Mos Def moniker. Shortly after that announcement, he recorded as the narrator of the children's hip hop musical, Pacha's Pajamas: A Story Written By Nature.


title: Mos Def

text: In January 2012, it was reported that Bey and Talib Kweli had begun "to resurrect" Black Star. In 2015, Bey was featured on A$AP Rocky's second studio album "At. Long. Last. ASAP", on the track "Back Home", alongside Acyde and the deceased A$AP Yams. Bey again revived his Mos Def moniker for two new songs in August 2015, titled "Basquiat Ghostwriter" and "Sensei on the Block", respectively.


title: Mos Def

text: On January 19, 2016, Bey announced his retirement from both the music and film industries on Kanye West's website: "I'm retiring from the music recording industry as it is currently assembled today, and also Hollywood, effective immediately. I'm releasing my final album this year, and that's that." After announcing his retirement, he expressed gratitude to everyone who has supported him over the years and revealed his intention to enter the fashion industry and complete a handful of films. Bey also confirmed he still planned to release a collaborative project with Ferrari Sheppard called Dec 99th.


title: Mos Def

text: In October 2016, a planned concert in London was cancelled due to travel restrictions imposed on the artist; other European dates suffered the same fate. On October 14, Bey posted a video to Facebook where he announced that he was still planning to retire: "I'm retiring for real this year, this week. With the 17th anniversary of "Black on Both Sides" being released, I am grateful to have had the career that I have been able to enjoy." He also announced one last concert which he said he would be live streaming from Cape Town, South Africa. In November 2016, he was granted the ability to leave but not reenter South Africa and was put on "South Africa's 'undesirable persons' list". He said he would perform one show in Harlem and three in Washington D.C. after leaving South Africa. He announced that Dec 99th, his final album, would be released on December 9. He released three singles from it, "Local Time", "N.A.W." and "Seaside Panic Room". On December 5, 2016, he announced the title of two albums, "Negus in Natural Person" and "As Promised", the latter of which is a collaboration with Southern hip hop producer Mannie Fresh, initially titled "OMFGOD". His claims of retirement were seen as questionable as he played shows on September 13, 2017, at the Fox Theater in Oakland as part of Black Star and performed on Gorillaz' Humanz World Tour, performing "Stylo" with Peven Everett, who filled in for Bobby Womack, who died in 2014. He also has yet to release or announce a release date for the last two albums of his career.


title: Mos Def

text: In February 2018, Bey announced, on stage, a new Black Star studio album, produced by Madlib, would be released in 2018. However, no specific release date was made available. Later on that year, Bey appeared on the titular track of "Kids See Ghosts", the collaborative effort of Kanye West and Kid Cudi. In March 2019, he debuted his album, "ንጉሥ (pronounced Negus)" at a listening session as part of Art Basel Hong Kong. In a press release, he said that the album "will continue to unfold as a series of varied installations around the world". He has no plans of releasing the album digitally or physically.


title: Mos Def

text: On June 28, 2019, Bey appeared on "Bandana", an album by Freddie Gibbs and Madlib, alongside Black Thought, on a track named "Education". In November 2019, he stated that unreleased music, such as his collaborative album with Mannie Fresh, was still "on deck" for release. In 2021, he launched "The Midnight Miracle" podcast on Luminary, along with Dave Chappelle and Talib Kweli. In April 2022, a release date for the long-awaited Black Star project was officially announced. The album titled "No Fear of Time" was released via Luminary on May 3, 2022.


title: Mos Def

text: Prior to his career in music, Bey entered public life as a child actor, having played roles in television movies, sitcoms and theater, some of which were under the name Dante Beze. At the age of 14, he appeared in the TV movie "God Bless the Child", starring Mare Winningham, which aired on ABC in 1988. He played the oldest child in the 1990 family sitcom "You Take the Kids", shortly before it was cancelled. In 1995, he played the character Dante, Bill Cosby's sidekick on the short-lived detective show "The Cosby Mysteries". In 1996, he starred in a Visa check card commercial featuring Deion Sanders. He also had a small role alongside Michael Jackson in his short film and music video "Ghosts" (1997).


title: Mos Def

text: After brief appearances in "Bamboozled" and "Monster's Ball", Bey played a rapper who is reluctant to sign with a major label in "Brown Sugar". He was nominated for an Image Award and a Teen Choice Award.


title: Mos Def

text: In 2001, he took a supporting role to Beyoncé Knowles and Mehki Phifer in the MTV movie "" as Lt. Miller, a crooked cop.


title: Mos Def

text: In 2002, he played the role of Booth in Suzan-Lori Parks' "Topdog/Underdog", a Tony-nominated and Pulitzer-winning Broadway play. He and co-star Jeffrey Wright won a Special Award from the Outer Critics Circle Award for their joint performance. He played Left Ear in the 2003 film "The Italian Job". That same year, he appeared in the Alicia Keys music video You Don't Know My Name.


title: Mos Def

text: In television, Bey has appeared on "NYPD Blue", Comedy Central's "Chappelle's Show", and hosted the award-winning HBO spoken word show "Def Poetry". He also appeared on the sitcom "My Wife and Kids" as the disabled friend of Michael Kyle (Damon Wayans).


title: Mos Def

text: Bey won "Best Actor, Independent Movie" at the 2005 Black Reel Awards for his portrayal of Detective Sgt. Lucas in "The Woodsman". For his portrayal of Vivien Thomas in HBO's film "Something the Lord Made", he was nominated for an Emmy and a Golden Globe, and won the Image Award. He also played a bandleader in HBO's "Lackawanna Blues". He then landed the role of Ford Prefect in the 2005 movie adaptation of "The Hitchhiker's Guide to the Galaxy".


title: Mos Def

text: In 2006, Bey appeared in "Dave Chappelle's Block Party" alongside Black Star partner Talib Kweli, while also contributing to the film's soundtrack. He was also featured as the banjo player in the Pixie Sketch" from "Chappelle's Show: The Lost Episodes", though his appearance was edited out of the DVD. He starred in the action film "16 Blocks" alongside Bruce Willis and David Morse. He also landed a recurring guest role on "Boondocks", starring as Gangstalicious. He is set to be in "Toussaint", a film about Haitian revolutionary Toussaint Louverture, opposite Don Cheadle and Wesley Snipes. He made a cameo appearance as himself in the movie "".


title: Mos Def

text: In 2008, Bey starred in the Michel Gondry movie "Be Kind Rewind", playing a video rental store employee whose best friend is played by co-star Jack Black. He also portrayed Chuck Berry in the film "Cadillac Records", for which he was nominated for a Black Reel Award and an Image Award.


title: Mos Def

text: In 2009, he appeared in the "House" episode titled "Locked In" as a patient suffering from locked-in syndrome. His performance was well received, with E! saying that Mos Def "delivers an Emmy-worthy performance". He was also in the 2009 film "Next Day Air".


title: Mos Def

text: In 2010, he appeared on the children's show "Yo Gabba Gabba!" as Super Mr. Superhero. He also appeared in "A Free Man of Color", John Guare's play at the Vivian Beaumont Theatre.


title: Mos Def

text: In 2011, he began a multi-episode appearance on the sixth season of Showtime television series "Dexter". He played Brother Sam, an ex-convict who has supposedly found religion despite finding himself in violent situations.


title: Mos Def

text: In January 2016, Bey announced his retirement from the music and the film industries on Kanye West's website. In March 2016, it was announced that he had been attached to star in "his last live-action film", "The Disconnected", a science fiction thriller dealing with policing, identity, and the intersection of technology and humanity.


title: Mos Def

text: In 2000, paired with Talib Kweli, Bey organized the Hip Hop for Respect project to speak out against police brutality. It was created in response to the 1999 police shooting of Amadou Diallo, and sought to accumulate 41 artists to the roster, one to match each of the 41 gunshots fired on Diallo.


title: Mos Def

text: Bey is well known for his leftist activism. In 2000, he performed a benefit concert for death row inmate Mumia Abu-Jamal. In May 2005, Bey, Talib Kweli, R&B singer Martin Luther and City Councilman Charles Barron approached New York City Hall, demanding the withdrawal of the $1 million bounty for Assata Shakur.


title: Mos Def

text: In September 2005, Bey released the single "Katrina Clap", renamed "Dollar Day" for "True Magic" (utilizing the instrumental for New Orleans rappers UTP's "Nolia Clap"). The song is a criticism of the Bush administration's response to Hurricane Katrina. On the night of the MTV Video Music Awards, Bey pulled up in front of Radio City Music Hall on a flatbed truck and began performing the "Katrina Clap" single in front of a crowd that quickly gathered around him. He was subsequently arrested for not having a public performance permit in his possession.


title: Mos Def

text: In October 2006, Bey appeared on "4Real", a documentary television series. Appearing in the episode "City of God", he and the 4Real crew traveled to City of God, a favela in Rio de Janeiro, Brazil, to meet Brazilian MC MV Bill and learn about the crime and social problems of the community.


title: Mos Def

text: On September 7, 2007, Bey appeared on "Real Time with Bill Maher" where he spoke about racism against African Americans, citing the government response to Hurricane Katrina, the Jena Six case, and the murder conviction of Mumia Abu-Jamal. He appeared on "Real Time" again on March 27, 2009, and spoke about the risk of nuclear weapons.


title: Mos Def

text: In September 2011, Bey joined the cast of the environmental children's hip hop musical "Pacha's Pajamas: A Story Written By Nature" as narrator. In July 2013, he appeared in a short film released by the human rights organization Reprieve, depicting the forced-feeding methods used at the Guantanamo Bay detention camps. This transpired after a document containing the military instructions for the procedure was leaked.


title: Mos Def

text: In September 2018, Bey and advertising executive Free Richardson opened an art exhibition to the public in an art gallery in the South Bronx, called the Compound, centered around hip-hop and fine art. The goal of this gallery was to help bridge the gap between the two fields, by showcasing artists from marginalized backgrounds who normally would not be represented in art galleries. Art forms with negative connotations, such as graffiti, as presented in a more optimal context. "The purpose of the gallery is to say all art is equal," Mr. Richardson said. "But we are in the borough that created hip-hop, which is the biggest art form in the world, so it's always an extending arm. It's always present."


title: Mos Def

text: About.com ranked him #14 on its list of the Top 50 MCs of Our Time, and "The Source" ranked him #23 on their list of the Top 50 Lyricists of All Time. AllMusic called him one of the most promising rappers to emerge in the late 1990s, and one of hip-hop's brightest hopes entering the 21st century. He has influenced numerous hip hop artists throughout his career, including Lupe Fiasco, Jay Electronica, Kid Cudi, and Saigon. Kendrick Lamar once mentioned him as a very early inspiration as a young rapper, though Lamar denied being a part of the conscious rap movement. He has also directly influenced artists outside of hip-hop, including English singer-songwriters Adele and Amy Winehouse.


title: Mos Def

text: Bey married Maria Yepes in 1996. He filed for divorce from Yepes in 2006. She took him to court over failure in child-support obligations, paying $2,000 short of the monthly $10,000 he is ordered to pay for their two daughters. He has four other children.


title: Mos Def

text: His mother Sheron "Umi" Smith has actively managed portions of her son's career. She is a motivational speaker, and authored the book "Shine Your Light: A Life Skills Workbook", where she details her experience as a single mother raising him.


title: Mos Def

text: In January 2016, Bey was ordered to leave South Africa and not return for five years, having stayed in the country illegally on an expired tourist visa granted in May 2013. That month, he was charged with using an unrecognized World Passport and having lived illegally in South Africa since 2014. He had reportedly recruited Kanye West to help defend him, and posted a message on West's website announcing his retirement from show business. There was an ongoing court case in relation to immigration offenses involving the artist and his family. He was allowed to leave South Africa on November 22, 2016, but he was barred from coming back.


title: Life expectancy

text: Life expectancy is a statistical measure of the average time an organism is expected to live, based on the year of its birth, current age, and other demographic factors like sex. The most commonly used measure is life expectancy at birth (LEB), which can be defined in two ways. "Cohort" LEB is the mean length of life of a birth cohort (all individuals born in a given year) and can be computed only for cohorts born so long ago that all their members have died. "Period" LEB is the mean length of life of a hypothetical cohort assumed to be exposed, from birth through death, to the mortality rates observed at a given year.


title: Life expectancy

text: National LEB figures reported by national agencies and international organizations for human populations are estimates of "period" LEB. In the Bronze Age and the Iron Age, human LEB was 26 years; in 2010, world LEB was 67.2 years. In recent years, LEB in Eswatini (formerly Swaziland) is 49, while LEB in Japan is 83. The combination of high infant mortality and deaths in young adulthood from accidents, epidemics, plagues, wars, and childbirth, before modern medicine was widely available, significantly lowers LEB. For example, a society with a LEB of 40 would have relatively few people dying at exactly 40: most will die before 30 or after 55. In populations with high infant mortality rates, LEB is highly sensitive to the rate of death in the first few years of life. Because of this sensitivity, LEB can be grossly misinterpreted, leading to the belief that a population with a low LEB would have a small proportion of older people. A different measure, such as life expectancy at age 5 (e), can be used to exclude the effect of infant mortality to provide a simple measure of overall mortality rates other than in early childhood. For instance, in a society with a life expectancy of 30, it may nevertheless be common to have a 40-year remaining timespan at age 5 (but perhaps not a 60-year one).


title: Life expectancy

text: Until the middle of the 20th century, infant mortality was approximately 40–60% of the total mortality. Excluding child mortality, the average life expectancy during the 12th–19th centuries was approximately 55 years. If a person survived childhood, they had about a 50% chance of living 50–55 years, instead of only 25–40 years.


title: Life expectancy

text: Aggregate population measures—such as the proportion of the population in various age groups—are also used alongside individual-based measures—such as formal life expectancy—when analyzing population structure and dynamics. Pre-modern societies had universally higher mortality rates and lower life expectancies at every age for both males and females. This example is relatively rare.


title: Life expectancy

text: Life expectancy, longevity, and maximum lifespan are not synonymous. Longevity refers to the relatively long lifespan of some members of a population. Maximum lifespan is the age at death for the longest-lived individual of a species. Mathematically, life expectancy is denoted formula_1 and is the mean number of years of life remaining at a given age formula_2, with a particular mortality. Because life expectancy is an average, a particular person may die many years before or after the expected survival.


title: Life expectancy

text: Life expectancy is also used in plant or animal ecology, and in life tables (also known as actuarial tables). The concept of life expectancy may also be used in the context of manufactured objects, though the related term shelf life is commonly used for consumer products, and the terms "mean time to breakdown" (MTTB) and "mean time between failures" (MTBF) are used in engineering.


title: Life expectancy

text: The longest verified lifespan for any human is that of Frenchwoman Jeanne Calment, who is verified as having lived to age 122 years, 164 days, between 21 February 1875 and 4 August 1997. This is referred to as the "maximum life span," which is the upper boundary of life, the maximum number of years any human is known to have lived. A theoretical study shows that the maximum life expectancy at birth is limited by the human life characteristic value δ, which is around 104 years. According to a study by biologists Bryan G. Hughes and Siegfried Hekimi, there is no evidence for limit on human lifespan. However, this view has been questioned on the basis of error patterns.


title: Life expectancy

text: Records of human lifespan above age 100 are highly susceptible to errors. For example, the previous world-record holder for human lifespan, Carrie C. White, was uncovered as a simple typographic error after more than two decades.


title: Life expectancy

text: The following information is derived from the 1961 "Encyclopædia Britannica" and other sources, some with questionable accuracy. Unless otherwise stated, it represents estimates of the life expectancies of the world population as a whole. In many instances, life expectancy varied considerably according to class and gender.


title: Life expectancy

text: Life expectancy at birth takes account of infant mortality and child mortality but not prenatal mortality.


title: Life expectancy

text: Life expectancy increases with age as the individual survives the higher mortality rates associated with childhood. For instance, the table above gives the life expectancy at birth among 13th-century English nobles at 30. Having survived to the age of 21, a male member of the English aristocracy in this period could expect to live:


title: Life expectancy

text: 17th-century English life expectancy was only about 35 years, largely because infant and child mortality remained high. Life expectancy was under 25 years in the early Colony of Virginia, and in seventeenth-century New England, about 40% died before reaching adulthood. During the Industrial Revolution, the life expectancy of children increased dramatically. The under-5 mortality rate in London decreased from 74.5% (in 1730–1749) to 31.8% (in 1810–1829).


title: Life expectancy

text: Public health measures are credited with much of the recent increase in life expectancy. During the 20th century, despite a brief drop due to the 1918 flu pandemic, the average lifespan in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health.


title: Life expectancy

text: Human beings are expected to live on average 30–40 years in Eswatini and 82.6 years in Japan. An analysis published in 2011 in "The Lancet" attributes Japanese life expectancy to equal opportunities, public health, and diet.


title: Life expectancy

text: There are great variations in life expectancy between different parts of the world, mostly caused by differences in public health, medical care, and diet. The impact of AIDS on life expectancy is particularly notable in many African countries. According to projections made by the United Nations in 2002, the life expectancy at birth for 2010–2015 (if HIV/AIDS did not exist) would have been:


title: Life expectancy

text: Actual life expectancy in Botswana declined from 65 in 1990 to 49 in 2000 before increasing to 66 in 2011. In South Africa, life expectancy was 63 in 1990, 57 in 2000, and 58 in 2011. And in Zimbabwe, life expectancy was 60 in 1990, 43 in 2000, and 54 in 2011.


title: Life expectancy

text: During the last 200 years, African countries have generally not had the same improvements in mortality rates that have been enjoyed by countries in Asia, Latin America, and Europe.


title: Life expectancy

text: In the United States, African-American people have shorter life expectancies than their European-American counterparts. For example, white Americans in 2010 are expected to live until age 78.9, but black Americans only until age 75.1. This 3.8-year gap, however, is the lowest it has been since 1975 at the latest. The greatest difference was 7.1 years in 1993. In contrast, Asian-American women live the longest of all ethnic groups in the United States, with a life expectancy of 85.8 years. The life expectancy of Hispanic-Americans is 81.2 years. According to the new government reports in the US, life expectancy in the country dropped again because of the rise in suicide and drug overdose rates. The Centers for Disease Control (CDC) found nearly 70,000 more Americans died in 2017 than in 2016, with rising rates of death among 25- to 44-year-olds.


title: Life expectancy

text: Cities also experience a wide range of life expectancy based on neighborhood breakdowns. This is largely due to economic clustering and poverty conditions that tend to associate based on geographic location. Multi-generational poverty found in struggling neighborhoods also contributes. In United States cities such as Cincinnati, the life expectancy gap between low income and high-income neighborhoods touches 20 years.


title: Life expectancy

text: Economic circumstances also affect life expectancy. For example, in the United Kingdom, life expectancy in the wealthiest and richest areas is several years higher than in the poorest areas. This may reflect factors such as diet and lifestyle, as well as access to medical care. It may also reflect a selective effect: people with chronic life-threatening illnesses are less likely to become wealthy or to reside in affluent areas. In Glasgow, the disparity is amongst the highest in the world: life expectancy for males in the heavily deprived Calton area stands at 54, which is 28 years less than in the affluent area of Lenzie, which is only away.


title: Life expectancy

text: A 2013 study found a pronounced relationship between economic inequality and life expectancy. However, in contrast, a study by José A. Tapia Granados and Ana Diez Roux at the University of Michigan found that life expectancy actually "increased" during the Great Depression, and during recessions and depressions in general. The authors suggest that when people are working at a more extreme degree during prosperous economic times, they undergo more stress, exposure to pollution, and the likelihood of injury among other longevity-limiting factors.


title: Life expectancy

text: Life expectancy is also likely to be affected by exposure to high levels of highway air pollution or industrial air pollution. This is one way that occupation can have a major effect on life expectancy. Coal miners (and in prior generations, asbestos cutters) often have lower life expectancies than average. Other factors affecting an individual's life expectancy are genetic disorders, drug use, tobacco smoking, excessive alcohol consumption, obesity, access to health care, diet, and exercise.


title: Life expectancy

text: In the present, female human life expectancy is greater than that of males, despite females having higher morbidity rates (see Health Survival paradox). There are many potential reasons for this. Traditional arguments tend to favor sociology-environmental factors: historically, men have generally consumed more tobacco, alcohol, and drugs than women in most societies, and are more likely to die from many associated diseases such as lung cancer, tuberculosis, and cirrhosis of the liver. Men are also more likely to die from injuries, whether unintentional (such as occupational, war, or car accidents) or intentional (suicide). Men are also more likely to die from most of the leading causes of death (some already stated above) than women. Some of these in the United States include cancer of the respiratory system, motor vehicle accidents, suicide, cirrhosis of the liver, emphysema, prostate cancer, and coronary heart disease. These far outweigh the female mortality rate from breast cancer and cervical cancer. In the past, mortality rates for females in child-bearing age groups were higher than for males at the same age.


title: Life expectancy

text: A paper from 2015 found that female fetuses have a higher mortality rate than male fetuses. This finding contradicts papers dating from 2002 and earlier that attribute the male sex to higher in-utero mortality rates. Among the smallest premature babies (those under ), females have a higher survival rate. At the other extreme, about 90% of individuals aged 110 are female. The difference in life expectancy between men and women in the United States dropped from 7.8 years in 1979 to 5.3 years in 2005, with women expected to live to age 80.1 in 2005. Data from the United Kingdom shows the gap in life expectancy between men and women decreasing in later life. This may be attributable to the effects of infant mortality and young adult death rates.


title: Life expectancy

text: Some argue that shorter male life expectancy is merely another manifestation of the general rule, seen in all mammal species, that larger-sized individuals within a species tend, on average, to have shorter lives. This biological difference occurs because women have more resistance to infections and degenerative diseases.


title: Life expectancy

text: In her extensive review of the existing literature, Kalben concluded that the fact that women live longer than men was observed at least as far back as 1750 and that, with relatively equal treatment, today males in all parts of the world experience greater mortality than females. However, Kalben's study was restricted to data in Western Europe alone, where the demographic transition occurred relatively early. United Nations statistics from mid-twentieth century onward, show that in all parts of the world, females have a higher life expectancy at age 60 than males. Of 72 selected causes of death, only 6 yielded greater female than male age-adjusted death rates in 1998 in the United States. Except for birds, for almost all of the animal species studied, males have higher mortality than females. Evidence suggests that the sex mortality differential in people is due to both biological/genetic and environmental/behavioral risk and protective factors.


title: Life expectancy

text: One recent suggestion is that mitochondrial mutations which shorten lifespan continue to be expressed in males (but less so in females) because mitochondria are inherited only through the mother. By contrast, natural selection weeds out mitochondria that reduce female survival; therefore, such mitochondria are less likely to be passed on to the next generation. This thus suggests that females tend to live longer than males. The authors claim that this is a partial explanation.


title: Life expectancy

text: Another explanation is the unguarded X hypothesis. According to this hypothesis, one reason for why the average lifespan of males isn't as long as that of females––by 18% on average, according to the study––is that they have a Y chromosome which can't protect an individual from harmful genes expressed on the X chromosome, while a duplicate X chromosome, as present in female organisms, can ensure harmful genes aren't expressed.


title: Life expectancy

text: Before the Industrial Revolution, men lived longer than women on average. In developed countries, starting around 1880, death rates decreased faster among women, leading to differences in mortality rates between males and females. Before 1880, death rates were the same. In people born after 1900, the death rate of 50- to 70-year-old men was double that of women of the same age. Men may be more vulnerable to cardiovascular disease than women, but this susceptibility was evident only after deaths from other causes, such as infections, started to decline. Most of the difference in life expectancy between the sexes is accounted for by differences in the rate of death by cardiovascular diseases among persons aged 50–70.


title: Life expectancy

text: The heritability of lifespan is estimated to be less than 10%, meaning the majority of variation in lifespan is attributable due to differences in environment rather than genetic variation. However, researchers have identified regions of the genome which can influence the length of life and the number of years lived in good health. For example, a genome-wide association study of 1 million lifespans found 12 genetic loci which influenced lifespan by modifying susceptibility to cardiovascular and smoking-related disease. The locus with the largest effect is APOE. Carriers of the APOE ε4 allele live approximately one year less than average (per copy of the ε4 allele), mainly due to increased risk of Alzheimer's disease.


title: Life expectancy

text: In July 2020, scientists identified 10 genomic loci with consistent effects across multiple lifespan-related traits, including healthspan, lifespan, and longevity. The genes affected by variation in these loci highlighted haem metabolism as a promising candidate for further research within the field. This study suggests that high levels of iron in the blood likely reduce, and genes involved in metabolising iron likely increase healthy years of life in humans.


title: Life expectancy

text: A follow-up study which investigated the genetics of frailty and self-rated health in addition to healthspan, lifespan, and longevity also highlighted haem metabolism as an important pathway, and found genetic variants which lower blood protein levels of LPA and VCAM1 were associated with increased healthy lifespan.


title: Life expectancy

text: In developed countries, the number of centenarians is increasing at approximately 5.5% per year, which means doubling the centenarian population every 13 years, pushing it from some 455,000 in 2009 to 4.1 million in 2050. Japan is the country with the highest ratio of centenarians (347 for every 1 million inhabitants in September 2010). Shimane Prefecture had an estimated 743 centenarians per million inhabitants.


title: Life expectancy

text: In the United States, the number of centenarians grew from 32,194 in 1980 to 71,944 in November 2010 (232 centenarians per million inhabitants).


title: Life expectancy

text: The mentally ill have been shown to have a 10- to 25-year reduction in life expectancy. Generally, the reduction of lifespan in the mentally ill population compared to the mentally stable population has been studied and documented.


title: Life expectancy

text: The greater mortality of people with mental disorders may be due to death from injury, from co-morbid conditions, or medication side effects. For instance, psychiatric medications can increase the risk of developing diabetes. It has been shown that the psychiatric medication olanzapine can increase risk of developing agranulocytosis, among other comorbidities. Psychiatric medicines also affect the gastrointestinal tract; the mentally ill have a four times risk of gastrointestinal disease.


title: Life expectancy

text: As of 2020 and the COVID-19 pandemic, researchers have found an increased risk of death in the mentally ill.


title: Life expectancy

text: The life expectancy of people with diabetes, which is 9.3% of the U.S. population, is reduced by roughly 10–20 years. People over 60 years old with Alzheimer's disease have about a 50% life expectancy of 3–10 years. Other demographics that tend to have a lower life expectancy than average include transplant recipients and the obese.


title: Life expectancy

text: Education on all levels has been shown to be strongly associated with increased life expectancy. This association may be due partly to higher income, which can lead to increased life expectancy. Despite the association, among identical twin pairs with different education levels, there is only weak evidence of a relationship between educational attainment and adult mortality.


title: Life expectancy

text: According to a paper from 2015, the mortality rate for the Caucasian population in the United States from 1993 to 2001 is four times higher for those who did not complete high school compared to those who have at least 16 years of education. In fact, within the U.S. adult population, people with less than a high school education have the shortest life expectancies.


title: Life expectancy

text: Preschool education also plays a large role in life expectancy. It was found that high-quality early-stage childhood education had positive effects on health. Researchers discovered this by analyzing the results of the Carolina Abecedarian Project, finding that the disadvantaged children who were randomly assigned to treatment had lower instances of risk factors for cardiovascular and metabolic diseases in their mid-30s.


title: Life expectancy

text: Various species of plants and animals, including humans, have different lifespans. Evolutionary theory states that organisms which—by virtue of their defenses or lifestyle—live for long periods and avoid accidents, disease, predation, etc. are likely to have genes that code for slow aging, which often translates to good cellular repair. One theory is that if predation or accidental deaths prevent most individuals from living to an old age, there will be less natural selection to increase the intrinsic life span. That finding was supported in a classic study of opossums by Austad; however, the opposite relationship was found in an equally prominent study of guppies by Reznick.


title: Life expectancy

text: One prominent and very popular theory states that lifespan can be lengthened by a tight budget for food energy called caloric restriction. Caloric restriction observed in many animals (most notably mice and rats) shows a near doubling of life span from a very limited calorific intake. Support for the theory has been bolstered by several new studies linking lower basal metabolic rate to increased life expectancy. That is the key to why animals like giant tortoises can live so long. Studies of humans with life spans of at least 100 have shown a link to decreased thyroid activity, resulting in their lowered metabolic rate.


title: Life expectancy

text: In a broad survey of zoo animals, no relationship was found between investment of the animal in reproduction and its life span.


title: Life expectancy

text: In actuarial notation, the probability of surviving from age formula_2 to age formula_4 is denoted formula_5 and the probability of dying during age formula_2 (i.e. between ages formula_2 and formula_8) is denoted formula_9 . For example, if 10% of a group of people alive at their 90th birthday die before their 91st birthday, the age-specific death probability at 90 would be 10%. This probability describes the "likelihood" of dying at that age, and is not the "rate" at which people of that age die. It can be shown that


title: Life expectancy

text: The "curtate future lifetime", denoted formula_10, is a discrete random variable representing the remaining lifetime at age formula_2, rounded down to whole years. Life expectancy, more technically called the "curtate expected lifetime" and denoted "formula_12 ," is the mean of formula_10—that is to say, the expected number of whole years of life remaining, assuming survival to age formula_2. So,


title: Life expectancy

text: If the assumption is made that, on average, people live a half year on the year of their death, the complete life expectancy at age formula_2 would be formula_16.


title: Life expectancy

text: By definition, life expectancy is an arithmetic mean. It can also be calculated by integrating the survival curve from 0 to positive infinity (or equivalently to the maximum lifespan, sometimes called 'omega'). For an extinct or completed cohort (all people born in the year 1850, for example), it can of course simply be calculated by averaging the ages at death. For cohorts with some survivors, it is estimated by using mortality experience in recent years. The estimates are called period cohort life expectancies.


title: Life expectancy

text: The starting point for calculating life expectancy is the age-specific death rates of the population members. If a large amount of data is available, a statistical population can be created that allow the age-specific death rates to be simply taken as the mortality rates actually experienced at each age (the number of deaths divided by the number of years "exposed to risk" in each data cell). However, it is customary to apply smoothing to remove (as much as possible) the random statistical fluctuations from one year of age to the next. In the past, a very simple model used for this purpose was the Gompertz function, but more sophisticated methods are now used. The most common modern methods include:


title: Life expectancy

text: The age-specific death rates are calculated separately for separate groups of data that are believed to have different mortality rates (such as males and females, or smokers and non-smokers) and are then used to calculate a life table from which one can calculate the probability of surviving to each age. While the data required are easily identified in the case of humans, the computation of life expectancy of industrial products and wild animals involves more indirect techniques. The life expectancy and demography of wild animals are often estimated by capturing, marking, and recapturing them. The life of a product, more often termed shelf life, is also computed using similar methods. In the case of long-lived components, such as those used in critical applications (e.g. aircraft), methods like accelerated aging are used to model the life expectancy of a component.


title: Life expectancy

text: It is important to note that the life expectancy statistic is usually based on past mortality experience and assumes that the same age-specific mortality rates will continue. Thus, such life expectancy figures need to be adjusted for temporal trends before calculating how long a currently living individual of a particular age is expected to live. Period life expectancy remains a commonly used statistic to summarize the current health status of a population. However, for some purposes, such as pensions calculations, it is usual to adjust the life table used by assuming that age-specific death rates will continue to decrease over the years, as they have usually done in the past. That is often done by simply extrapolating past trends, but some models exist to account for the evolution of mortality, like the Lee–Carter model.


title: Life expectancy

text: As discussed above, on an individual basis, some factors correlate with longer life. Factors that are associated with variations in life expectancy include family history, marital status, economic status, physique, exercise, diet, drug use (including smoking and alcohol consumption), disposition, education, environment, sleep, climate, and health care.


title: Life expectancy

text: To assess the quality of these additional years of life, 'healthy life expectancy' has been calculated for the last 30 years. Since 2001, the World Health Organization has published statistics called Healthy life expectancy (HALE), defined as the average number of years that a person can expect to live in "full health" excluding the years lived in less than full health due to disease and/or injury. Since 2004, Eurostat publishes annual statistics called Healthy Life Years (HLY) based on reported activity limitations. The United States uses similar indicators in the framework of the national health promotion and disease prevention plan "Healthy People 2010". More and more countries are using health expectancy indicators to monitor the health of their population.