Voyage of Rediscovery

By James P. Delgado

Initial Targets

Days after stepping off the research vessel Nautilus on another collaborative mission in the Gulf of Mexico, I was in Honolulu and then, with Hans, riding on the deck of the tugboat taking the LRT to sea with Pisces V lashed to its deck. A quick inflatable ride took us from the tug to the LRT, where we pulled off our dive boots and scrambled in bare feet into the six-foot-diameter sphere that is the heart of the Pisces . Terry Kerby cranked the hatch shut, and we settled into position in front of three small ports, gazing into the blue water while the LRT team slowly ballasted their craft. As the LRT sank and leveled, they undid the lashings for the Pisces V , and Terry piloted the vessel off the submerged deck.

We watched the sonar screen as the Pisces V slowly descended, the water going to deep blue and then black as the temperature dropped. Our first dives were on a pair of familiar targets, two Japanese Type A midget submarines, one of them sunk by the crew of the USS Ward (DD-139) early on 7 December 1941. NOAA’s Office of National Marine Sanctuaries’ Maritime Heritage Program works closely with the National Park Service’s Submerged Resources Center to monitor the Ward midget as a war grave and historic site. We also examined the other Type A sub, lying in three disarticulated pieces. Terry Kerby’s exhaustive research indicates that she is also a Pearl Harbor attack-associated craft.

Two new targets proved to be wrecks. We slowly made out the form of the first, lying in more than 2,000 feet of water, after passing over a bright blue hedgehog practice projectile. A single mast was still standing proud, and an old-fashioned ship’s wheel on the poop deck remained in position. The antique style and strange gear at the bow quickly gave Hans’ memory a jog, and he was sure she was the long-forgotten USS Kialua (IX-71), originally the cable-layer Dickenson, built in 1923 and chartered by the Navy in 1942.

The Kailua and her crew worked hard as a fleet auxiliary, serving from Pago Pago, Samoa, to Milne Bay, New Guinea, as the Dictionary of American Naval Fighting Ships notes, “laying cables, ASW nets, and buoys.” Returning to Pearl Harbor in July 1944, she worked there until decommissioned on 29 October 1945. In July of the next year, the Kailua was sunk by torpedoes off Oahu, her exact location not recorded. But our identification was cinched after we carefully navigated around the bow, dodged dangling cables, and found a faded white IX-71 still painted on the hull.

Super Sub Spotted

During our dive on the fourth target, we were lying flat (or nearly so, as you need to flex slightly in the submersible’s sphere) and silently gazing out the ports into the darkness as the Pisces V ’s lights picked out forms of rocks littering the muddy bottom. There was a gradual slope, and then suddenly, the mangled bow of a submarine came into view, with a long, thick cable draped across the deck. Terry powered the Pisces up, clearing the cable, and we started a slow drive over the deck, heading aft. The submarine was huge, and badly damaged.

The characteristic launching ramp for seaplanes common to Japan’s Type B and larger I-400 -class submarines was present, as was a hull-mounted crane for retrieving aircraft after flight. But the massive hangar and sail were missing, leaving only a mass of wreckage including exposed deck frames, piping, and a dislodged hatch. Unlike HURL’s 2005 discovery of the I-401 , sister ship of the I-400 , there was no intact conning tower with the sub’s identifying hull number painted on it. The aft deck gun remained in place, though, as did the stern. The hull was imploded, the aft hatch popped open. The damage to the bow also was evidence of a violent sinking; the bow of the submarine was detached, twisted off to port, and the exposed torpedo tubes so badly mangled it would take hours of carefully studying video of the dive to discern that there were indeed the characteristic eight tubes, four over four, that armed the bow of the I-400 .

Flying solo without another submersible to provide cover and with no means for help meant we did not venture too close to the wreck or off to its sides, where loose piping and cables might have snagged us. Nevertheless, we systematically studied all that we could see. The hangar and sail probably lie off to the starboard side and in deeper water, where we did not venture.

The thrill of discovery is followed by a great deal of work—submersible recovery and cleaning, recharging of batteries, replacement of air-filtration packs, and comparison of notes. As the HURL team prepped the Pisces V and LRT, and then readied them for winter lay-up, Steve and Terry joined Hans and me as we pored over old photographs and drawings as well as the footage and still photographs from our dive. There was no clear “smoking gun” to say the second wreck was the I-400 , but gradually a number of points of convergence made clear that it was the long-lost super submarine. Terry’s report on the wreck noted the exact match of the deck gun, aircraft crane, torpedo tubes, aft running light, and finally the dimensions, shorter than they should have been in the sonar because some 30 feet of the bow had torn free.

When the I-400 was used as a target during 1946 tests of remotely guided torpedoes, she took hits forward and midships and went down by the bow, striking bottom after a short and fast glide. The impact imploded the unflooded or partially flooded stern and tore the bow free. The submarine settled on more or less an even keel in some 2,300 feet of water but miles away from the rough coordinates the Navy provided. This was likely deliberate. A nascent Cold War foe, the Soviet Union, was demanding access to the I-400 and I-401 on the grounds that any Japanese military technology should be made available to all Allied powers. But in the case of the super subs, that was not going to happen—either on the surface or below.

The rediscovery of the I-400 made global news. Like other finds of lost ships, it struck a responsive chord with many who learned about a largely forgotten or ignored piece of history, despite two recent and excellent books on the amazing I-400 -class submarines (John Geoghegan’s Operation Storm and Henry Sakaida, Gary Nila, and Koji Takaki’s I-400 ). The find also sparked discussions and reminiscences from those in Japan and the United States involved with these craft. Moreover, it reminded us that the world’s greatest museum is at the bottom of the sea. Unlike other vessels lost to the scrap yard, the historic ships that sank and were once thought forever lost still remain with us. They are special places that reflect our past and hopefully compel us to continue to explore a part of the planet that desperately needs our attention.

Japan’s Giant Subs

By Norman Polmar

The largest undersea craft of the first half-century of modern submarine development and operations were the Imperial Japanese Navy’s I-400 -class boats—aircraft-carrying giants designed specifically to launch floatplane bombers against U.S. cities. Between the two world wars, several nations experimented with launching aircraft from submarines, but only the Japanese navy actually flew submarine-launched aircraft during World War II. Missions included two incendiary raids by a floatplane from the submarine I-25 against Oregon forests in August 1942. These were the only air strikes against the continental United States during the war.

Design of the I-400 began in 1942, with plans calling for a surface displacement of some 4,500 tons—almost twice that of the largest submarine built for the U.S. Navy, the Argonaut (SM-1/SS-166), completed in 1928. The Japanese craft was to carry two large floatplanes that would be launched by a catapult built into the outer hull structure. Subsequently, the envisioned submarine was enlarged to carry three aircraft plus parts for a fourth.

The submarine had a large conning tower incorporated into a hangar structure. Forward of the tower was an 85-foot, 4-inch catapult track, slightly offset to starboard. A folding crane forward could recover floatplanes that came alongside the submarine. Aircraft could be warmed up in the long, narrow hangar while the submarine was submerged through a system circulating heated lubricating oil.

An Aichi M6A plane would be pulled from the hangar onto the catapult, and the wings and tail sections unfolded and floats attached. The aircraft would then be armed and launched. Four trained crewmen could prepare a plane for flight in about seven minutes.

Deck guns and torpedo tubes were fitted, providing the submarines with potent self-defense/attack capabilities. Other I-400 features included radar and snorkel. The craft could carry sufficient fuel to cruise farther than any non-nuclear submarine—37,500 nautical miles at 14 knots on the surface.

The I-400 program originally was to provide 19 aircraft-carrying submarines, the I-400 through I-417 plus one unnamed unit. The lead boat was laid down on 18 January 1943. As the war progressed, Japanese shipbuilding programs were continually cut back, and only three of the submarines were completed, the first, the I-400 , in December 1944, and the others in January and July 1945. The final one, the I-402 , was modified during construction to serve as a submarine tanker to carry oil from the East Indies through the U.S. submarine blockade to the Home Islands.

In 1943 the Japanese began developing plans for the I-400 and I-401 plus smaller plane-carrying submarines to carry out attacks with ten aircraft against the Panama Canal. And, reportedly, a plan was being developed to use submarine aircraft for germ-warfare attacks against the U.S. West Coast. Then a multi-submarine, suicide air attack against the U.S. forces at Ulithi Atoll was planned for August 1945. But the war ended before these underwater giants could carry out any attacks.

Like most Japanese warships that survived the war, the I-400 s had an ignominious end. All three submarines surrendered to U.S. forces in August 1945—approaching American warships on the surface, flying a black flag, and having jettisoned all torpedoes and ammunition.

The I-402 was the first to die, being scuttled off the Goto Islands in the East China Sea on 1 April 1946. The I-400 and I-401 were manned by American crews and sailed (on the surface) to Guam and then on to Pearl Harbor. After being carefully examined by submarine specialists, both were sunk as targets off Oahu, on 4 June and 31 May 1946, respectively—by U.S. submarine torpedoes.

Mr. Polmar, a columnist for Naval History and Proceedings , is coauthor, with Dorr Carpenter, of Submarines of the Imperial Japanese Navy 1904–1945 (Naval Institute Press, 1986).

I-400-class Submarine

Displacement: 5,223 tons surface

6,560 tons submerged

Length: 400 feet, 3 inches

Beam: 39 feet, 4 inches

Draft: 23 feet

Propulsion: 4 diesel engines (7,700 horsepower)

2 electric motors (2,400 horsepower)

2 shafts

Speed: 18.75 knots (surface)

6.5 knots (submerged)

Armament: 8 21-inch torpedo tubes (bow); 20 torpedoes

1 14-cm (5.5-inch) deck gun

10 25-mm deck guns (3 triple; 1 single)

Aerial munitions: 4 torpedoes

3 1,760-pound bombs

12 550-pound bombs

Complement: 144 officers and enlisted men



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