The Aichi AC-1 was an experimental 250 kW (330 hp) nine-cylinder air-cooled radial engine.
In 1929, it was used to power the newly designed Aichi AB-2, a catapult-launched reconnaissance seaplane.
This was a major turning point, not only for Aichi, but for all of the other Japanese aircraft and engine manufacturers, as they no longer need rely on foreign designs.
[1] The engine proved to be a disappointment by not performing as expected.
On one test flight, an exhaust fire spread to the airframe and the aircraft was lost, and, soon after, the project ended.