In 1943, the scarcity of Packard Merlin engines necessitated that the Allison engine be reintroduced yet again into the P-40 production line. The result was the P-40M version.
The P-40M was essentially similar to the P-40K-20-CU, apart from the use of the Allison V-1710-18 engine, rated at 1200 hp for takeoff and 1125 hp at 17,300 feet. The P-40M could be distinguished from the P-40K by the introduction of a cooling grill forward of the exhaust stubs.
The P-40M was built solely for Lend-Lease, the contract being approved on August 24, 1942. The first P-40M appeared in November, 1942. Most of them went to the RAF, the RAAF, and the RNZAF as the Kittyhawk III. The type served with British Commonwealth forces in the Far East. A number were operated in Italy by No. 5 Squadron of the South African Air Force.
The differences between the production blocks were as follows:
The P-40M-1-CU had reinforced ailerons.
The P-40M-5-CU had improved carburetor air filters and further aileron improvements.
The P-40M-10-CU had revised undercarriage warning systems and fuel system changes
Serials of the P-40M were as follows:
43-5403/5462 Curtiss P-40M-1-CU Warhawk 43-5463/5722 Curtiss P-40M-5-CU Warhawk 43-5723/6002 Curtiss P-40M-10-CU Warhawk
The RAF serials for the 264 P-40Ms supplied to the RAF as Kittyhawk IIIs were FR779/FR872 and FS100/FS269.
168 P-40Ms were supplied to Australia as Kittyhawk IIIs under the serial numbers A29-300/389, A29-400/414, A29-420/434, A29-442/460, and A29-473/502.
34 P-40Ms went to New Zealand as serial numbers NZ3066/3073, NZ3075/3089, NZ3109/3119, and NZ3180
The P-40M equipped the No. 5 Squadron of the South African Air Force serving in Italy.
19 P-40Ms were transferred to Brazil.