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 Maiden flight April 1939. The aircraft's unusual design featured its 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 firing through the center of the propeller hub. Entry to the cockpit was through a side door. Total 9,584 example were produced, with over half being sent to the Soviet Union under the lend-lease program.