In September 1940, Britain ordered 386 P-39Ds (Model 14), with a 20 mm (.79 in) Hispano-Suiza HS.404 and six .303 in (7.7 mm), instead of a 37 mm (1.46 in) cannon and six 0.30 in (7.62 mm) guns.
The RAF eventually ordered a total of 675 P-39s.
However, after the first Airacobras arrived at 601 Squadron RAF in September 1941, they were promptly recognized as having an inadequate rate of climb and performance at altitude for Western European conditions.
Only 80 were adopted, all of them with 601 Squadron.
Britain transferred about 200 P-39s to the Soviet Union.

Another 200 examples intended for the RAF were taken up by the USAAF after the attack on Pearl Harbor as the P-400, and were sent to the Fifth Air Force in Australia, for service in the South West Pacific Theatre.

By the time of the Pearl Harbor attack, nearly 600 P-39s had been built.
When P-39 production ended in August 1944, Bell had built 9,558 Airacobras, of which 4,773 (mostly −39N and −39Q) were sent to the Soviet Union through the Lend-Lease program.
There were numerous minor variations in engine, propeller, and armament, but no major structural changes in production types, excepting a few two-seat TP-39F and RP-39Q trainers.
In addition, seven went to the U.S. Navy as radio-controlled drones.

Trials of a laminar flow wing (in the XP-39E) and Continental IV-1430 engine (the P-76) were unsuccessful.
The mid-engine, gun-through-hub concept was developed further in the Bell P-63 Kingcobra.

A naval version with tailwheel landing gear, the XFL-1 Airabonita, was ordered as a competitor to the Vought F4U Corsair and Grumman XF5F Skyrocket.
It first flew 13 May 1940, but after a troublesome and protracted development and testing period, it was rejected.
In September 1940, Britain ordered 386 P-39Ds (Model 14), with a 20 mm (.79 in) Hispano-Suiza HS.404 and six .303 in (7.7 mm), instead of a 37 mm (1.46 in) cannon and six 0.30 in (7.62 mm) guns. The RAF eventually ordered a total of 675 P-39s. However, after the first Airacobras arrived at 601 Squadron RAF in September 1941, they were promptly recognized as having an inadequate rate of climb and performance at altitude for Western European conditions. Only 80 were adopted, all of them with 601 Squadron. Britain transferred about 200 P-39s to the Soviet Union.
Another 200 examples intended for the RAF were taken up by the USAAF after the attack on Pearl Harbor as the P-400, and were sent to the Fifth Air Force in Australia, for service in the South West Pacific Theatre.
By the time of the Pearl Harbor attack, nearly 600 P-39s had been built. When P-39 production ended in August 1944, Bell had built 9,558 Airacobras, of which 4,773 (mostly −39N and −39Q) were sent to the Soviet Union through the Lend-Lease program. There were numerous minor variations in engine, propeller, and armament, but no major structural changes in production types, excepting a few two-seat TP-39F and RP-39Q trainers. In addition, seven went to the U.S. Navy as radio-controlled drones.
Trials of a laminar flow wing (in the XP-39E) and Continental IV-1430 engine (the P-76) were unsuccessful. The mid-engine, gun-through-hub concept was developed further in the Bell P-63 Kingcobra.
A naval version with tailwheel landing gear, the XFL-1 Airabonita, was ordered as a competitor to the Vought F4U Corsair and Grumman XF5F Skyrocket. It first flew 13 May 1940, but after a troublesome and protracted development and testing period, it was rejected.
Bell P-39 Airacobra