Submarine Bomber Aichi

M6A "Seiran" The submarine bomber was supposed to combine high speed with a long range, but since the aircraft was actually intended for one-time use, the type of chassis was not even specified. The diameter of the hangar of the submarine aircraft carrier was set at 3.5 m, while the aircraft had to fit in it without disassembly - the planes could only be folded.

At the beginning of 1943, six M6A1s were laid down at the Aichi plant in Nagoya, two of which were made in a training version of the M6A1-K on a wheeled chassis (the plane was called "Nanzan" - "South Mountain"). The aircraft, with the exception of the tip of the keel, hardly differed from the basic version, even retained the attachment points to the catapult.

The structure of the aircraft was all-metal, with the exception of the plywood sheathing of the wing tips and fabric sheathing of the steering surfaces. Two-slot all-metal flaps could be used as air brakes. The crew of two was housed under a single canopy. In the rear of the cockpit, from January 1943, it was decided to install a 13 mm "Type 2" machine gun, which was served by a radio operator. The offensive armament consisted of an 850 kg torpedo or one 800 kg or two 250 kg bombs.

Powerplant. Atsuta-21 is a licensed version of the early modifications of the 12-cylinder liquid-cooled Daimler-Benz DB-601 engine.

From the very beginning, it was envisaged to use detachable floats - the only dismountable part of the Seyran. Since the floats significantly reduced the flight performance of the aircraft, if necessary, the possibility of dropping them in the air was provided. In the hangar of the submarine, respectively, a place was provided for attaching the removed floats.

In early 1942, the Japanese High Command issued an order to shipbuilders for the largest submarines ever built until the beginning of the atomic era in shipbuilding. It was planned to build 18 submarines. During the design process, the displacement of such a submarine increased from 4125 to 4738 tons, the number of aircraft transported on board increased from three to four.

The first production aircraft M6A1 was ready in October 1944, another 7 aircraft were built by December 7, when the aircraft was seriously damaged as a result of an earthquake. By the spring, production was almost restored, but on March 12, an American air raid followed. The plant was again partially destroyed, and soon the production of "Seirans" was discontinued. The main reason for this decision was the problems with the production of the required number of submarines. Instead of 44 originally planned aircraft, until the end of the war, only 28 units were built, including prototypes and wheeled M6A1-K.

Combat use . At the end of autumn 1944, the Imperial Navy began to train pilots for "Seyrans", the flight and technical personnel were carefully selected. The preparations were carried out in an atmosphere of the highest secrecy. On December 15, the 631st Air Corps was created under the command of Captain Totsunoke Ariizumi. The corps was part of the 1st submarine flotilla, which consisted of only two submarines - I-400 and I-401. The flotilla consisted of 10 Seyans. In May, the flotilla was joined by submarines I-13 and I-14, which were involved in the training of the crews of the Seyrans. During six weeks of training, the release time of three "Seyrans" from the submarine was reduced to 30 minutes, including the installation of floats, however, in battle it was planned to launch aircraft without floats from a catapult, which took 14.5 minutes.

The original purpose of the 1st Flotilla was the Panama Canal locks. Six planes were to carry torpedoes and the other four bombs. Two aircraft were allocated to attack each target. The flotilla was to follow the same route as the Nagumo squadron during the attack on Perl Harbor three and a half years earlier. But it soon became clear that even if successful, such a raid was absolutely pointless to influence the strategic situation in the war. As a result, on June 25, an order was issued to send the 10th Submarine Flotilla to attack American aircraft carriers on Ulithi Atoll. On August 6, I-400 and I-401 left Ominato, but soon a fire broke out on the flagship due to a short circuit. This forced the start of the operation to be postponed until August 17, two days before which Japan surrendered. But even after that, the headquarters of the Japanese fleet planned to carry out an attack on 25 August. However, on August 16, the flotilla was ordered to return to Japan, and four days later - to destroy all offensive weapons. On I-401, the planes were ejected without starting the engines and without crews, and on I-400, they were simply pushed into the water. Thus ended the history of the most unusual scheme of the use of naval aviation during the Second World War.

Photo	Description
	Drawing M6A1
	Drawing M6A1-K
	Hangar on the submarine I-400 for M6A1

Bibliography

• Japan float aircraft /Evgeniy Aranov/
• "Japan Aircraft of World War II." /Oleg Doroshkevich/
• Aviation of Japan /Andrey Firsov/

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The plane was designed to bomb US targets that no conventional bomber could reach. It was supposed to build submarines, surpassing everything created before - especially for transporting and launching attack aircraft. A flotilla of such submarines was supposed to cross the Pacific Ocean, immediately before the chosen target, launch their aircraft, and then submerge. After the attack, the planes had to go out to meet with the submarine aircraft carriers, and then, depending on the weather conditions, the way to rescue the crews was chosen. After that, the flotilla sank again under the water.
Further, the submarines had to either go out to meet the supply vessels to receive new aircraft, bombs and fuel, or act in the usual way, using torpedoes.
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