During World War II, the United States provided more Bell P-39 Aircobras to the Soviet Union through Lend-Lease, than any other aircraft. The P-39 became the most popular foreign plane imported because of the remarkable success enjoyed by Soviet airmen, notably by Aleksandr I. Pokryshkin and pilots of his division, who flew and fought on the eastern front. The first P-39s to arrive in the Soviet Union, were the export variants, which the Americans began to turn out for England in August 1941. These were the Aircobra Is, fitted with 20-mm guns. Even as they tried to master the new American fighter, the Royal Air Force uncovered many defects and tried hard to improve them, but after a brief period of modifications, the RAF handed over eleven of its P-39s to the Soviets, shipping the planes via convoys to the USSR through northern ports.
