


BB-61 Iowa-class Design

These were among the most powerful warship ever assembled. Previous battleships had to give up performance in either speed, armor, or firepower in order to achieve better results in the other two. The designers of the Iowa class attempted to produce a design that made no such sacrifices.


The Iowa class design was conceived in an era of crisis. As the United States crept ever more closely to officially entering the Second World War, its Navy faced some major problems with its ship inventory. Much of war planning is based on "what if?" scenarios. These are situations where there is a small chance that the enemy could do something that will turn the tide of a future war against your forces.

Specifically, friend and foe alike had outclassed the Navy's battleship inventory and by the late 1930's, the Navy realized that it faced many nightmarish "what if" situations. It was in this environment that designers and policy makers within the Navy Department conceived the Iowa-class battleships.

Even though many people recognized that battleships were becoming obsolete and that aircraft carriers were more important, America's disadvantage in battleship design was not an easy concept to ignore. US Navy intelligence had reached the unfortunate conclusion that Japan and Germany might very well dump everything agreed to in previous arms limitation treaties such as the 1919 Treaty of Versailles, the 1922 Washington Naval Treaty, the London Naval Treaty of 1936. These treaties limited the size, armanent, and the aggregate tonnage of the world's ships.

The United States faced two specific problems: the German battleship Bismarck and the Japanese titan Yamato. Additionally, the two Axis nations were very busy building a series of new heavy cruisers and "pocket" battleships to back up the larger capital ships. Japan had just finished a class of cruisers, called the Kongo-class, capable of 30 knots. These cruisers would be able to outrun anything in the American fleet. Despite assurances from Hitler to the West, the German navy had launched several new ships that ignored various international agreements.

The United States' latest designs, however, respected the limitations established in the various arms limitation treaties. The United States was not about to be the first one to pull out of the arms conventions. As a result, the only upgrade in design for the North Carolinas and South Dakotas was an increase in armament from 14-inch guns to Mk6 16-inch/45 caliber rifled guns.

In January 1936, the Japanese government publicly renounced the latest round of naval limitation treaties. With this announcement, the United States responded by beginning work on a new, much larger 45,000-ton battleship design. The responsibility for coming out with a new design fell to the Navy's Battleship Design Advisory Board (BDAB). Formed in 1936 through an executive order, this group was made up of America's finest maritime architects. For this specific project, Capt. Allan Chantry, manager of the Philadelphia Navy Yard's Industrial Development, was the lead designer. Chantry was one an intellectually brilliant officer. He graduated first in his class at the Naval Academy in 1906 and received his master's degree at the Massachusetts Institute of Technology in Cambridge, MA. Before he began work on Wisconsin, Chantry oversaw the construction of the battleships Washington (BB-56), New Jersey (BB-62), and several aircraft carriers.

With the decision made to design and build a new class of battleships, the numbers game began. The design of any battleship had to consider three basic factors: speed, firepower, and armor.

Conventional wisdom said that a designer had to sacrifice performance in one category in order to gain performance in the other two. For example, the designers of USS North Carolina (BB-54) originally called for the battleship to have 12 14-inch guns. However, they decided to upgrade the firepower of the ship by equipping her with nine 16-inch guns, still wanted the 35,000-ton vessel (the maximum displacement under the Washington Naval Treaty) to be able to steam at 28 knots. As a result, North Carolina 's armor was relatively light and was only able to stop a 14-inch shell.

Some improvements were made with the South Dakota-class but only with some ingenious and creative engineering as both of these battleships were also restricted to 35,000-tons. These two warships had to be the same displacement as North Carolina, but with increased armor protection and the same speed. The result was a shorter, slightly fatter hull.

Bismarck and Yamato, however, still equaled or outclassed all current American designs in one or more factors. Additionally, the fast heavy cruisers, such as Kongo and the German Scharnhorst, posed a "what if" scenario where enemy warships played havoc with American shipping. Once Navy intelligence confirmed this, BDAB was faced with the task of building a battleship class capable of chasing down and defeating anything it might meet. The board set out to build a class of battleship that equalled or exceeded all enemy designs in every category. While BDAB could now build warships without treaty restrictions, American designers still had a special restriction to work through. Any American warship had to be able to fit through the Panama Canal so it would not have to make marathon runs between the Atlantic and the Pacific like USS Oregon (BB-3) had to do in 1898. As a result, the new class of battleship could not exceed 110 feet at the beam.

BDAB set the following parameters for the next class of ships. Each ship was to cost about $125 million to build, be constructed and commissioned in about three and half years, and displace about 52,000-tons (fully loaded). Originally, Congress would only agree to build two ships out of the Iowa-design. The new design gave Congress sticker shock, as the vessels were 60% more expensive than previous designs. However, the crisis brought on by the fall of France led Roosevelt to demand a two ocean fleet. Congress agreed to Roosevelt's demand and authorized four more ships. It was out of this emergency spending that the Iowa class came to life. Congress even considered authorizing an even larger class of warship because of the grave crisis.


With the fixed factors in mind, the first consideration was the main armament. BDAB had four options. Option number one was to match the Yamato (the biggest battleship facing the Americans) gun for gun with the Mk1 18-inch/45 caliber rifle. This monster gun, the largest ever assembled in America, could fire a two-ton shell several miles that could penetrate 16 inches of armor. There were several problems with using this weapon (option number one called for the use of nine Mk1s.) It would slow the ships down to a snail crawl of 22 knots, add six months to construction time, require that some of the armor be shed on the turrets, and most importantly, the beam of the ship would have to be increased to 131 feet in order to accommodate the sheer size of the guns.

Option number two was to have only dual mounted 18-inch guns. While it might have saved some space and displacement, BDAB quickly dismissed this option. It would have required additional design and test work, being that there was no dual mount available.

Options number three and four both considered the use of the smaller 16-inch rifles. There were two types available: the Mk6 16-inch/45 caliber rifle that was used on both North Carolina and South Dakota and the newer Mk7 16-inch/50 caliber rifle. While the Mk6 would make the designer's job easier because it was small and light, the Mk6 would not solve the firepower problem. Option 4, the Mk7 16-inch/50 caliber rifle, was a good compromise of firepower, size, weight, and cost.

The Mk7 had several other advantages over the other options. During a rapid-fire situation, the Mk7 could fire twice as fast as the 18-inch guns and would give the new class a further reach than the older Mk6 16-inch rifles. Additionally, the turrets for the Mk7 could be given sufficient armor to withstand an incoming 16-inch shell, unlike the Mk1 18-inch guns. Fully equipped, each of Wisconsin's triple mounted turrets weighed over 2,100 tons. At 6,300 tons, these three turrets alone made up about 12% of the ship's displacement.

The Naval Gun Factory (Building 76 and present site of the Navy Museum.) at the Washington Navy Yard located in Southeast Washington, DC designed and manufactured the guns. The installation of the nine Mk7 16-inch/50-caliber guns was among the most complicated procedures performed. With the skill of a surgeon, each gun had to be installed within a 1/4-inch of standards. Each gun, not including the gun breech, weighed around 120 tons (considered to be a "lightweight" design) and could fire a one ton shell 24 miles.

World War II battleships had a concern that their older Spanish-American War and World War I counterparts did not have to worry about: air attacks. Despite the modern battleship's classification as "dreadnought" battleships (which meant among other things that the vessel carried an all big gun arrangement), designers equipped their warships with several smaller caliber guns. From the start, these ships were to have 20 5-inch/38 caliber dual purpose guns mounted in 10 turrets. These guns could put up 22 shells per minute per gun in the anti-aircraft role. The Naval Gun Factory designed the smaller guns, but contracted their manufacture to other factories.

Designers initially gave the Iowa-class 20 Mk12 five-inch "dual purpose" guns installed in 10 gun mounts for secondary armament. Even though the keels had already been laid, designers continued to tweak the design. One of the things that made World War II different than most previous wars was that the combatants more quickly learned lessons of the battlefield and applied them to new weapon designs. The first instance was the British use of the antique Swordfish bi-plane in a torpedo bomber role. In 1940, Swordfish knocked out the Italian battlefleet and in 1941 is same bi-plane disabled Bismarck during her famous breakout sortie. The second event was the infamous Japanese air attack on Pearl Harbor on December 7, 1941. Further battle experience, such as the naval fights around Guadalcanal, gained by American battleships only reinforced the need for more secondary guns.

The very real threat of air attacks forced designers to place several smaller AA guns. Additional guns were to be placed to supplement the dual mounted five-inch guns. Twenty Mk2 quad mounted 40mm Bofers, 29 20mm single mounted guns, and several .50 caliber machine guns were added. The problem with adding such an impressive array of guns was that the ship would require an additional 1,900 sailors to an already cramped ship. Despite this problem, the risk of air attack was too great and the additional guns, and sailors, were ordered.


The second basic factor, after firepower, to be considered was Iowa class armor. The armor scheme was a copy of the armor used on North Carolina and South Dakota, only thicker. This armor could, in theory, stop a 16-inch shell coming in at a 45-degree angle. There was some idle talk about making the Iowa class armor tough enough to stop an 18-inch shell, but BDAB dropped the idea when it realized how much more weight and redesign work it would take.

Nickel-steel was used to manufacture the armor. This type of steel is a kind of stainless steel which has the added benefits that it does not corrode quickly, but bends easily. Nickel-steel was not a new material. From the start, armored warships like USS Indiana (BB-1) used this type of steel. One 17 1/2 inch belt of the nickel-steel ran from the deck to the below water line on both sides of the ship and covered the middle 2/3 of the ship. Eighteen inch plates were used in the turrets and 11 1/2 inch plates were placed on the decks.

It is interesting to note that much of the Iowa class's armor is just as thick as battleships built 50 years earlier. Wisconsin and her sisters, however, benefitted from advances in steel technology that allowed mills to forge the steel at higher temperatures and heat treatment, which in turn produced a much higher quality steel that was stronger and more elastic. Two plants, Bethehelm Steel's main mill in Bethehelm, PA and Luken Steel's Coatsville mill just ouside Phildadelphia, manufactured most of the armor plating. For the turret plate, however, a special forge was constructed just for the Iowa-class at the Charleston Ordnance Works in Charleston, WV.


Armor and guns weighed the ships down considerably, which under normal circumstances would have meant the ship would not be able to achieve a very high rate of speed. BDAB, however, set a very high bar for Iowa and her sisters. BDAB wanted the new class of warships to steam at 33-knots. This would make them the fastest battleships ever built. They would be four knots faster than Bismarck, eight knots faster than the Yamato, and just as fast as any potential commerce raider. To achieve such speed, the hull of Iowa-class ships is over 200 feet longer than the North Carolina-class and South Dakota-class.

Additionally, workers installed the largest conventional engineering plant ever assembled on US Navy ships. They were given twelve Foster Wheeler boilers along with Westinghouse manufactured engines. Together, the boilers and engines turned out over 220,000 ship horsepower on four shafts. This power plant continue to be the envy of Navy engineers to this day. This is not only due to their size, but also because they operated at 600 pounds per square inch. This lower pressure makes them very reliable, though it tends to make the ship somewhat of a fuel hog. The redundancy was unbelievable. Something could break down, which was rare, and no one would ever know the difference.

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Page last modified: 22-07-2011 17:35:48 ZULU