Australia, Britain, France, Italy, Portugal, Soviet Union, United Kingdom, and the United States used the P-39.
France ordered some P-39s but they were taken over by the United Kingdom.
Royal Air Force Disappointed
The RAF tested the P-39 but it didn't perform up to the standards of the British fighters at the time. However, 675 were ordered, but only the No. 601 Squadron received them. 250 of them were sent to the Soviet Union.
Fighting With the United States
The United States needed to use any available fighters against Japan in 1942 and 1943 and in the early combat in the Middle East.
The first combat was in April 1942 against the Japanese.
The 12th Air Force, in the Middle East, used P-39s for straffing. They were also used to support landings in Tunisia, Sicily, and Italy.
"Shaving" With the Soviet Union
Approximately 5,000 (4,773, 4,925) were supplied to the Russians and they were nick named "Shaving" as it was slang for ground strafing. It was well liked for its ability to destroy German vehicles.
The Soviets replaced the American armament with the 20 mm B-20 cannon and 12.7 mm UBS machine guns.
Free French and Italian Co-Belligerent
Some French and Italian pilots (of the Italian co-belligerent Air Force in 1944) also flew the P-39.
The Australians used 22 P-39s.
During the early months of the Korean War the North Korean Peoples' Air Force had some P-39s.