Flights From the By Norman Polmar and Kenneth J. Moore WO revolutionary weapons were introduced early in the 20th century: the airplane and the submarine. Com- bining the two took some imagina- tion and lots of ingenuity. TThe first rudimentary steps toward the combination took place during World War I. The British and Ger- man navies used standard subma- rines that carried floatplanes on the surface that would then submerge just enough to float off the aircraft. After carrying out their mission, the plane. France built the submarine Attempts to launch aircraft aircraft would return to a land base cruiser Surcouf with large guns to from submarines date to or put down at sea, where they were attack merchant ships and a floatplane World War I. Between the scuttled after the pilots were recov- to search out targets. The US Navy world wars, Britain used a ered. modified the submarine S-1 for ex- modified submarine monitor, M2. By World War II, Japan Between the world wars, three periments with a collapsible float- had taken the lead in sub- other countries began to take an in- plane that could be stowed in a han- launched aircraft capabilities. terest in placing aircraft on subs. gar on deck. France, Japan, and the United States The more extensive work, how- experimented with subs and float- ever, was begun in 1923 by Japan. It planes. Their approaches varied, and, first used two German Caspar–Heinkel while most efforts might be described U-1 biplanes, fitted with floats, to as dilettante, Japan managed to pro- conduct trials aboard a submarine. It duce a system in World War II that then developed a series of floatplanes could deliver an aircraft to within for submarine use, beginning with striking distance of the US main- the Watanabe Type 96 (E9W1), which land. entered service in 1938. This biplane Britain continued its earlier work, aircraft and the monoplane Yokosuka converting the large submarine moni- Type 0 (E14Y1), which entered ser- tor, designated M2, to carry a float- vice in 1941, had far-reaching ser- 68 AIR FORCE Magazine / March 2004 War produces many strange results. The submersible aircraft carrier was one. Deep Photos courtesy Norman Polmar vice in the Pacific in the early years mission, the crew would land the On these two missions, both pi- of World War II. (The Yokosuka aircraft in the water alongside the loted by Warrant Flying Officer Type 0 was given the Allied codename submarine, where it would be hoisted Nobuo Fujita, the aircraft flew about Glen.) aboard by a crane. 50 miles inland, where Fujita re- By the start of World War II, These airplanes flew missions leased incendiaries. The missions Japan’s Navy had 12 large I-series throughout the southwest Pacific and failed. There were no major fires submarines that could each carry a Indian Ocean areas, seeking Allied and no casualties. single floatplane. Japan didn’t stop shipping and performing reconnais- These were the only known air- there. It had more aircraft-carrying sance of Allied ports. craft attacks mounted against the con- submarines under construction, of tinental United States during the war. which several became operational To the United States Japan also employed large subma- during the war. In 1942, Japan extended opera- rines to refuel seaplanes, including The new subs had hangars for a tions to the US mainland. two flying boats that bombed Pearl single, disassembled floatplane, with The Japanese submarine I-25 twice Harbor on the night of March 3-4, a catapult built into the deck. The launched a Yokosuka Type 0 mono- 1942. submarine surfaced, the crew ex- plane from a position off Cape Blanco, Japan continued to pursue the sub- tracted the aircraft from the hangar, Ore., on incendiary bombing raids marine-aircraft combination, build- extended the wings, prepared it for against the United States. The goal ing even larger subs intended to carry flight, and catapulted the airplane was to ignite forest fires in the north- aircraft to bomb Washington, D.C., off the sub. After completing their western United States. and New York City. AIR FORCE Magazine / March 2004 69 In 1942, Japan began construction tion to carry fuel from the East Indies bomb. The Seiran could be launched of the I-400 class—the Sen-Toku to Japan. The war ended before the without the pylon-attached floats, but (STo) or special submarines. These I-402 undertook a tanker mission. then the pilot would have to ditch at were the largest non-nuclear subma- Japan launched a fourth, the I-404, sea. Without the large pylons and rines ever constructed. They had a but work on the sub stopped in March floats, the aircraft could carry one surface displacement of 5,223 tons 1945 when it was 90 percent com- torpedo or 1,760-pound bomb or two and were 400.25 feet long—a length plete. US carrier-based aircraft sank 551-pound bombs. not exceeded by submarines until the I-404 at Kure, Japan, on July 28, During practice, the time to un- the nuclear-propelled submarines of 1945. None of the other 12 I-400s fold the aircraft’s wings and tail sur- the mid-1960s. The I-400s were pro- reached the launching stage. faces and ready it for launching—in pelled on the surface by diesel en- darkness—was less than seven min- gines and submerged by electric Unique Aircraft utes. The three aircraft could be read- motors, which obtained their energy Complications also arose with the ied for flight and launched within 30 from batteries. aircraft—the high-performance Aichi minutes of the submarine coming to While the first I-400s were under M6A1 Seiran floatplane—that Japan the surface. Although, even at night, construction, the changing course of was building for the I-400 subma- this was a long time for the subma- the Pacific war caused Japan to rines. The Seiran, which translates rine to be exposed, it was a remark- change the I-400 mission from strikes to “mountain haze,” would be the able achievement. on Washington and New York City world’s only attack aircraft built The giant submarine had a maga- to the Panama Canal. Japan wanted specifically to operate from subma- zine that could hold four aerial tor- to slow the flow of US warships into rines. (The Allies did not learn of the pedoes, three 1,760-pound bombs, the Pacific. aircraft until after the war, so it had and 12 550-pound bombs. Beyond The original 1942 design of the no Allied codename.) its aircraft weapons, each I-400 was I-400 provided a hangar to accom- The single-engine Seiran was 38 armed with eight 21-inch torpedo modate two floatplanes, but it was feet long and 15 feet high, with a tubes forward and carried 20 torpe- enlarged to handle three aircraft. The wingspan of just more than 40 feet. does. Each sub also had one 5.5-inch aircraft hangar, beneath the conning It weighed 7,277 pounds empty. It deck gun and 10 smaller anti-air- tower, opened to an 85.4-foot cata- had to fit inside an 11.5-foot cylin- craft guns. pult track forward of the hangar. The der-shaped hangar, so a ground crew Japan also modified two slightly aircraft were pre-warmed in the han- rotated the wings, then folded them smaller AM-class submarines, the gar, while the submarine was still to lie flat alongside the fuselage. I-13 and I-14, to embark two M6A1 submerged, by circulating heavy lu- They could also fold each side of the aircraft. The I-13 and I-14 were in- bricating oil through their engines. horizontal stabilizer and the vertical tended to operate with the I-400s in The submarine then surfaced to launch stabilizer part way. long-range air strikes. aircraft. The aircraft’s initial specifications Finally, on July 26, 1945, the I-400 Japan planned 18 of the I-400 class called for no undercarriage. There and I-401—with their six attack air- submarines, completing the first in were provisions for support pylons craft—sortied from the Inland Sea December 1944. The I-401 and I-402 with floats that would enable the to strike the US naval anchorage at followed in 1945. However, the I-402 aircraft to land on the water but lim- Ulithi Atoll in the Caroline Islands was converted to a tanker configura- ited its payload to one 551-pound in an operation called Hikari. The I-13 Photos courtesy Norman Polmar One of Japan’s large I-series submarines twice used submarine-launched Warrant Flying Officer Nobuo Fujita aircraft to mount attacks against the US mainland. These were the only manned was the pilot for both of Japan’s attacks against any part of the 48 contiguous states during World War II. 1942 incendiary attacks on the US. 70 AIR FORCE Magazine / March 2004 and I-14 preceded them, each with two aircraft to fly from Truk Island to scout the lagoon at Ulithi before the attack. (The I-13 was sunk be- fore reaching the area.) However, the war in the Pacific ended on Aug. 15, two days before the planned strike. The submarines Photos courtesy Norman Polmar returned to Japan to be surrendered, along with their sister ships, to US forces. Japanese plans for these underwa- ter aircraft carriers—had the war con- tinued—included replacing their Seiran aircraft with Baka rocket-propelled suicide aircraft. There were uncon- firmed reports of proposals to use the submarines to launch aircraft carrying biological agents against the United States.