In May 1941, the production lines at Curtiss were busy with a new P-40 model--the P-40D (Model H87A-2).
The P-40D introduced a new engine, the Allison V-1710-39 of 1150 hp. This engine had originally been proposed for the experimental XP-46 fighter, but the USAAC had decided not to interrupt the P-40 production lines for a new type and decided instead to adapt the new engine to the existing P-40. Substitution of the modified P-40 for the experimental P-46 was proposed on June 10, 1940, and Curtiss agreed to adapt the basic P-40 to the new engine. The designation P-40D was assigned to the new project. The P-40D was considered sufficiently different from previous P-40 versions that it was allocated a new company designation by Curtiss--Model 87.
The P-40D introduced a new shorter nose design that was retained by all subsequent P-40s. The 1150 hp V-1710-39 engine had spur gear reduction that raised the thrust line by six inches, giving a completely different nose geometry. The overall length was reduced by six inches, the cross section of the fuselage was reduced, and the undercarriage was shortened. The radiator was increased in size and moved forward. Some 175 pounds of armor were added. The fuselage guns were deleted, and two 0.50-inch machine guns with new hydraulic chargers were installed in each wing. There were additional provisions in the wings for two 20-mm cannon, but these were never actually used. Shackles were added under the belly to accommodate a 51-gallon auxiliary fuel tank or a 500-pound bomb. Wing rack attachment points were provided for six 20-pound bombs. Gross weight of the D model was increased to 8670 pounds. The climb rate and ceiling consequently continued to remain poor.
Even before the first P-40D had been built, the United Kingdom ordered 560
examples for the RAF in May of 1940. The airframe and engine changes justified
a new name--Kittyhawk I. An unspecified number of Model 87s had also been ordered by
France, but were never delivered. They were designated Model 87A-1 by the company, but
this designation was cancelled after France fell. The following is a list of RAF
serials for the Kittyhawk I:
AK571/AK870 c/n 14952/15251 AK871/AK950 c/n 15342/15421 AK951/AK999 c/n 18695/18743 AL100/AL230 c/n 18744/18874These deliveries took place in late 1941. The first 20 Kittyhawk Is had four 0.50-inch machine guns mounted in the wings and were designated Model 87A-1, but the remaining Kittyhawk Is had six wing guns, and were designated Model 87A-2. These were identical to USAAF P-40Es with the exception of their use of British equipment.
Bruce Robertson says that 24 of these were diverted to the Royal Canadian Air Force. However, Bowers lists Canadian serials 1028/1099 as being assigned to these Kittyhawks, which comprises 72 aircraft. AK601, AK636, AK680, AK726,AK778, AK882, AK931, AK939, AK960, AK971, AK992, AK995, AL102, AL178, AL186, AL188, and AL203 were diverted to Turkey.
The USAAF did not actually order the P-40D into production until September of 1940, nearly 5 months after the RAF had ordered the equivalent Kittyhawk I. The US Army serials were 40-359/381 (c/ns 13234/13256).