Only extant Seiran (Clear Sky Storm) on display at Udvar-Hazy Center. This is the last of 28 built that was ferried by Lt. Kazuo Akatsuka to Yokosuka and surrendered in 1945. Designed by Toshio Ozaki who planned the B7A Ryūsei, the floatplane was powered by a 12-cyl liquid-cooled 1,400 hp Atsuta 32 engine that was a licence-built DB601A. These aircraft of 631 Kokutai were to be launched via catapult from 122 m I-400-class submarines capable of carrying three Seirans. Operations were planned to bomb Panama Canal, the US fleet at Ulithi Atoll and US cities, forestalled by the end of the war.

Some reports show MSN/Serial to be one and the same, another report lists serial as 28

The only surviving and last airframe built of the Seiran.

No Seiran (Clear sky Storm) ever saw combat but was intended to fulfill the requirement for a bomber that could operate from a submarine to strike directly at the US and strategic targets such as the Panama Canal. This is the last built as well as the only surviving airframe and is now on display at the NASM Udvar-Hazy Center.

Designed with folding wings and tail surfaces to be catapulted from submarines and used to attack the USA mainland, the first mission with Seirans on board was at sea when Japan surrendered. To shorten the launching process, they were to be catapulted from a cold start by heating the engine oil to 60°C in a separate chamber and pumping it through the engine just before launch, along with hot water. This is the only survivor of 28 built

The M6A1 Seiran was designed to emerge from large I-400 class submarines to bomb the locks in the Panama Canal. It never happened. This one received US Navy tail number 47 after capture. Note the Nakajima Kikka jet fighter, inspired by the Me 262, in the background.