World War II Database

Contributor: C. Peter Chen

ww2dbaseThe M6A Seiran submarine-launched torpedo seaplanes were designed in response for a 1942 requirement for aircraft to be used in conjunction with the I-400-class submarine carriers of the Japanese Navy. They were of an all-metal construction, with control surfaces covered in fabric. The design was done so that two or three of them could be stowed aboard their submarine carriers, used to attack targets in surprise. Despite the complex folding system with their tails and wings, a seasoned crew could prepare all three aircraft for launch within 30 minutes. They made use of water-cooled engines, rather than air-cooled engines more prevalent in the Japanese Navy air service, so that they could be warmed up in their hangars while the submarine was still under water; this allowed their mother submarines to remain on the ocean surface for a smaller amount of time. Because the submarines would have no means to recover these seaplanes after a mission is carried out, the thought was that the submarine carriers would rescue the air crews and abandon the aircraft. The first prototype took flight over Ise Bay, Japan in 1943; although the test flight failed due to a non-responsive horizontal tail stabilizer, it nevertheless generated much interest with the Japanese naval leadership, who would soon issue an order for 42 combat aircraft and 2 trainer aircraft. It was around this time when the name Seiran was given, which was inspired by a 18th century woodblock print titled "Awazu no seiran". The Japanese Navy formed 631st Naval Air Group to operate these submarine-borne seaplanes. The group initially operated at Kure, Japan, but the presence of surrounding mountains which posed danger led to the relocation of the group by Yashiro Island further south in mid-Mar 1945. Shortly after, they joined their submarine carriers at Nanao on the coast of the Sea of Japan. Although the original vision for M6A Seiran attack aircraft involved dropping bombs on New York, New York, United States to demoralize the American people or destroying the top of the Gatun Locks thus using the power of water to seriously damage the Panama Canal, no such mission would ultimately be executed; planning for such strikes was canceled in early Jun 1945 in favor of targets closer to Japan. In Jul 1945, two I-400-class submarines each carrying three M6A1 Seiran aircraft and two modified AM-class submarines each carrying two M6A1 Seiran aircraft were sent on an attack on the American anchorage of Ulithi in the Caroline Islands, but the Japanese surrender was announced before the task force reached their target, and the mission was ultimately aborted. Thus, none of the M6A Seiran aircraft were ever used in combat.

ww2dbaseIn all, 29 aircraft of this design were built, including 8 M6A1 prototypes, 18 M6A1 production aircraft, 2 M6A1-K Nanzan land-based trainers, and 1 M6A2 prototype. Production ceased in Jul 1945.

M6A Seiran Timeline

SPECIFICATIONS

M6A1

Machinery	One Aichi Atsuta Type 32 inverted V-12 liquid-cooled engine rated at 1,400hp
Armament	1x12.7mm Type 2 machine gun, 1x torpedo or 800kg of bombs
Crew	2
Span	12.26 m
Length	11.64 m
Height	4.58 m
Wing Area	27.00 m²
Weight, Empty	3,362 kg
Weight, Loaded	4,250 kg
Weight, Maximum	4,445 kg
Speed, Maximum	474 km/h
Speed, Cruising	296 km/h
Service Ceiling	9,900 m
Range, Normal	1,190 km

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