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Aichi M6A1 Seiran: Japan’s Submarine-Launched Panama Canal Bomber

4 August 2022

Aichi M6A1 Seiran: Japan’s Submarine-Launched Panama Canal Bomber, Robert C. Mikesh, 1975, ISBN 0-914144-13-8, 32 pp.

Aichi created Seirans to be based from the world’s only class of submarine aircraft carriers—the Imperial Japanese Navy I-400 Class. This makes the Seiran the only purpose-built submarine based attack aircraft, to date, and it is an aircraft with beautiful lines. Each I-400 Class submarine could support three aircraft and could be armed with torpedoes or bombs.

Aichi’s Seiran (晴嵐 Clear Storm Sky), more directly meaning an unexpected storm coming out of the clear blue sky, was a World War II (WW II) special mission-built aircraft with unique capabilities which was designed and built for the Imperial Japanese Navy (IJN). It was also unknown to the Allies during the war and may have totally surprised (living up to its name, Seiran) the Allies in any of the IJN’s envisioned mission scenarios. Serious mission planning and preparation to destroy the Panama Canal’s Gatun Lock (to deny easy access to the Pacific Ocean from the USA’s shipyards on its eastern, Atlantic, coast) was overtaken by events, changing the mission to instead attack aircraft carriers at anchor within the Ulithi Atoll (in readiness for the invasion of the Japanese Home Islands).

Little is known of the aircraft as it never was used in combat due to WW II’s sudden ending with the atomic bombing of Nagasaki which curtailed the only I-400 class/Seiran mission. Japan’s military aimed to destroy all plans and remaining aircraft (some production aircraft were lost in training and transport) at war’s end but one aircraft remained as did scattered bits of information.

Enter Robert C. Mikesh! His expertise in Japanese military aviation history as well as researching skills soon focused on the Seiran after WW II’s ending. His passion and abilities would eventually aid in his obtaining the curatorship of the National Air & Space Museum. There could hardly be a better person to write a treatise on this aircraft.

Mikesh does not disappoint. Various descriptions of the aircraft design aspects are both poetic as well as vividly clear. Photographs are many, non-repetitive and reinforce the concise text. Black and white line drawings fill in what the images cannot and the center two pages are a lovely art illustration of a float mounted Seiran done by Thomas Hitchcock. Mikesh does not stop there, though what has been mentioned is already exceptional, he also includes a dozen nostalgic color images from when the sole surviving Seiran was on outdoor display at NAS Alameda. Aichi M6A1 Seiran ends with eight tables of technical and performance data—seven for the Seiran with the last one for the I-400 Class submarine.

Printed in 1975 it was a bargain at the listed price but sells on the used market for 10x the original retail and still worth every penny. Mikesh was an exceptional author as well as aviation historian who was a perfect fit for writing this monograph about this unique aircraft—the world’s only purpose built submarine based attack aircraft. 

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