Watch the surrender of a I-400 class Supersubmarine.

Admiral Isoroku Yamamoto called for the construction of 18 of the massive submarines carrying a total of 36 attack planes. The name of the special submarine class was abbreviated to Sen-toku.

The attack planes had to be designed from scratch. The need for speed, range and a decent sized bomb payload required tradeoffs. The wings had to be foldable to fit inside the tube, or hangar, atop the submarine. The design work, testing, and building of the plane was outsourced to the Aichi Aircraft Company.

The I-400 program did have its detractors in the heavily bureaucratic Imperial Japanese Navy.  After the defeat at Midway in early June 1942, Japan became more focused on defending the homeland and far less on possible attacks on the U.S. mainland using the large submarines. The death of Yamamoto in mid-April 1943, played further into the hands…