Beginning in 1925, the United States began designing a special torpedo for purely aerial operations. The project was discontinued and revived several times, and finally resulted in the Mark 13 torpedo, which went into service in 1935. The Mark 13 differed from aerial torpedoes used by other nations in that it was wider and shorter. It was slower than its competitors but it had longer range. The weapon was released by an aircraft traveling lower and slower ( high, than its Japanese contemporary.