The Bell P-39 "Airacobra" was one of the principal fighter aircraft in service with American forces at the start of World War II. It was build by the Bell Aircraft Corporation. Its maiden flight was in April 1939. The aircraft's unusual design featured an Allison engine mounted in the middle of the fuselage, just behind the pilot, driving the propeller through a driveshaft passing between the pilot's feet. A 37 mm T9 cannon fired through the center of the propeller hub. Entry to the cockpit was through a side door. A Total of 9,584 examples were produced, with over half being sent to the Soviet Union under the lend-lease program.