Despite the success of the Merlin engine in the Warhawk, parallel production of the Allison-powered version continued owing to the limited supplies of the license-built British engine.
The P-40K series marked the introduction of the more powerful Allison V-1710-73 (F4R) engine rated at 1325 hp for takeoff and 1150 hp at 11,800 feet. This engine had an automatic boost control.
On October 28, 1941, 600 P-40Ks were ordered for Lend-Lease supply to China. It was envisaged that this would be the last P-40 model to be built in quantity, the P-60 replacing the P-40 on the Curtiss production lines thereafter. However, delays in the P-60 program caused the order for P-40Ks to be increased to a total of 1300 aircraft on June 15, 1942.
The first P-40K model rolled off the production line in August 1942. For some odd reason, the company model number used for the P-40K is unknown.
The P-40K-1-CU and P-40K-5-CU were generally similar to late-production P-40Es except for the more powerful Allison engine. The K-5 added rotary valve cooling. The K-1 and K-5 retained the short fuselage of the P-40E, but with the extra power there was a tendency to swing during takeoff and a dorsal fin was added to correct this problem. The P-40K-10s and later production blocks had the longer fuselage that was introduced on the P-40F-5-CU. The P-40K-15-CU was winterized.
The maximum speed of the P-40K was 320 mph at 5000 feet and 362 mph at 15,000 feet. A climb to 15,000 feet took 7.5 minutes. Range was 350 miles with a 500-pound bomb attached. Ferry range was 1600 miles. Weights were 6400 pounds empty, 8400 pounds gross, and 10,000 pounds maximum. Most of the P-40Ks served with the US forces in Asia and the Pacific and under Lend-Lease with the Chinese Air Force.
192 P-40K-1-CUs were diverted to England under Lend-Lease as Kittyhawk III. RAF serials were FL875/FL905, FR111/FR115, FR210/FR361, and FL710/FL713. The first examples were delivered to the Middle East in late 1942.
Forty-two P-40Ks served with the RAAF under serials A29-164/202 (P-40K-10-CU) and A29-203/205 (P-40K-15-CU). P-40Ks servicing with the RNZAF were NZ3045/3065, NZ3090, and NZ3099. Nine P-40K-1-CUs served with the RCAF under US Army serial numbers 42-45921, 45944, 45945, 45951, 45952, 45954, 45977, 46003, and 46004.
25 P-40Ks were diverted to Brazil
The serials for the P-40Ks were as follows:
42-9730/9929 Curtiss P-40K-5-CU Warhawk 42-9930/10264 Curtiss P-40K-10-CU Warhawk 42-10265/10429 Curtiss P-40K-15-CU Warhawk 42-45722/46321 Curtiss P-40K-1-CU Warhawk
The P-40K-1 had originally been assigned serials 42-65902/66501. The P-40K-5 thru -15 were originally assigned serials 42-64502/65201. These were all cancelled and reassigned as shown above.
One P-40K-10-CU, 42-10219, was fitted with an Allison V-1710-43 and used to develop some proposed P-40 improvements under the designation XP-40K. Experiments with cowling and relocated cooling systems altered the appearance of the aircraft from time to time. One such modification produced an aircraft with radiators in a swollen wing center section and a slim, pointed nose.