Bell P-400 Airacobra
The Royal Air Force (RAF) model was at first named "Caribou". During July 1941, the American nicname "Airacobra" was adopted. The P-400 designation had, in fact, been associated with the British Airacobras for contractual purposes as early as August 1941.
The P-400 Airabora was the export version of the Bell Aircobra, virtually identical
to the American P-39D, but the 37mm cannon was replaced
with a faster-firing and more reliable Hispano 20mm cannon with 60
rounds. The engine of
the Model 14 was the 1150 hp Allison V-1710-E4 (-35).
RAF serial numbers assigned to the P-400 Airacobra:
AH570/AH739 (170 planes)
AP264/AP384 (121 planes)
BW100/BW183 (84 planes)
BX135/BX434 (300 planes)
At the start of the Pacific War, the United States found itself in desperate need of aircraft and nearly 200 of the British direct-purchase Airacobras still in the United States were requisitioned by the USAAF. Although they were similar to the P-39D Airacobra, they were not identical and were known by the USAAC under the non-standard designation P-400, retaining their original RAF serial numbers and three-color camouflage scene. Most of these planes were used for training stateside, but some of them were rushed to the Pacific and used during early 1942.
In England, 179 P-400 Airacobras sent to Britain were requisitioned by the USAAF, assigned to the 12th Air Force and sent to North Africa.
Joe Baugher "Airacobra I for RAF, P-400"