Seiran

Seiran is a Japanese term that is commonly interpreted as meaning “clear sky” or “blue skies,” and it has been used as a name for various things in Japanese history. The best-known use is the Aichi M6A Seiran, a World War II–era submarine-launched floatplane developed for the Imperial Japanese Navy. The aircraft was designed to be carried by submarines of the I-400 class and launched at sea to attack Allied shipping and bases, enabling surprise strikes far from Japan’s shores. It featured a compact, folding-wing design suitable for stowage inside a submarine’s hangar and carried a small offensive payload.

The Seiran program remained largely experimental. Only a limited number of aircraft were built, and a few flew in trials in 1945 before Japan’s surrender. The concept exemplifies late-war Japanese interest in extending reach through submarine-based air power, combining naval mobility with aerial strike capability. Although the M6A Seiran did not achieve operational success, it influenced later discussions of maritime aviation and the broader exploration of submarine aviation concepts.

Outside of the aircraft’s historical significance, Seiran has appeared as a name in various cultural contexts, though such uses are less standardized. In historical and technical discussions, Seiran is most closely associated with the M6A floatplane and the wartime experimentation with submarine-launched air forces, representing one of the era’s ambitious but ultimately limited wartime innovations.