At the outbreak of the Pacific War, many large-sized submarines of the Imperial Japanese Navy were equipped with catapult and small observation-type aircraft desiged to attack harbors and to bomb the U.S. mainland. Acknowledging the success of former attacks by the Imperial Japanese Navy, it decided to plan surprise attack missions to the Panama canal by special submarineborne aircraft at the beginning of 1942. The plane was the Aichi M6A1 Seiran, designed exclusively fot this one exceptional mission. The Seiran was to be carried by the I-400 class submarine in a special hanger tube. 28 Seirans were produced in total by 1945.