By the summer of 1943, the performance of the P-40 Warhawk was leaving much to be desired, especially in comparison to the later types such as the P-38, P-47, and P-51 which were beginning to come into service. The P-40N version (company designation Model 87V, 87W) was introduced at this time in an effort to improve the capabilities of the basic design and thus avoid interrupting Curtiss production lines by having the company introduce an entirely new type. The first 1500 examples of this new Warhawk line were to have been delivered as P-40Ps powered by Merlin engines, but shortages of the Packard-built Merlin caused this order to be cancelled and the P-40N with the 1200 hp Allison V-1710-81 engine to be substituted in its place.
A new lightweight structure was introduced, two of the six wing-mounted guns were removed, smaller and lighter undercarriage wheels were installed, head armor was reintroduced, and aluminum radiators and oil coolers were installed. The resulting reduction in the weight, along with the use of the same V-1710-81 engine as used in the P-40M, made the P-40N the fastest of the P-40 series, reaching a speed of 378 mph at 10,500 feet. Even though by 1943 standards the Warhawk was rapidly becoming obsolescent, the P-40N became the version that was most widely built--5220 examples rolling off the Curtiss lines before production finally ceased.
There were several production blocks of the P-40N, which differed from each other as follows:
The first production block was the P-40N-1-CU. It appeared in March of 1943, still powered by the Allison V-1710-81 engine, but with 122 gallons of internal fuel and a generally lighter structure than its predecessors. With weight reduced to 6000 pounds empty, 7400 pounds gross, and 8850 pounds maximum, the N-1 was the fastest P-40 service variant and was intended for high altitude combat. Maximum speed was 378 mph at 10,500 feet and service ceiling was 38,000 feet. An altitude of 15,000 feet could be attained in 6.7 minutes. Armament consisted of four 0.50-inch machine guns in the wings. Four hundred P-40N-1-CUs were built.
The P-40N-5-CU variant introduced a modified cockpit canopy with a frameless sliding hood and a deeper, squared-off rectangular aft transparent section to improve the rearward view. This cockpit canopy was retained for all the rest of the production blocks of the N version. The N-5 version restored the full six-gun wing armament, since pilots had complained that four guns were insufficient. Underwing racks were fitted for bombs or drop tanks, increasing external stores capacity to 1500 pounds. The new heavier gross weight of 8350 pounds limited top speed to 350 mph at 16,400 feet and service ceiling to 31,000 feet. An altitude of 14,000 feet could be attained in 7.3 minutes. Range was 340 miles with a 500-pound bomb underneath the fuselage. Three drop tanks promised a ferry range of up to 3100 miles at 198 mph.
The P-40N-6-CU was the designation given to N-5s modified in the field and fitted with reconnaissance cameras in the fuselage.
The P-40N-10-CU production block aircraft were winterized aircraft. It had a faster climb rate, made possible by the removal of two wing guns.
The P-40N-15-CU production block aircraft differed in having the battery located forward of the firewall and new landing lights. The full six wing guns were installed, and larger capacity wing tanks were fitted.
The P-40N-20-CU introduced the V-1710-99 engine, which was simply an -81 powerplant with an automatic engine control unit.
The P-40N-25-CU differed from the N-20 only in having a revised instrument panel and in having non-metal self sealing fuel tanks.
The P-40N-26-CU was the designation given to N-25s fitted with reconnaissance cameras in the fuselage.
Three P-40N-25-CUs were converted as two-seat trainers under the designation RP-40N-26-CU.
On February 14, 1944, another thousand Warhawks were ordered, broken down into a batch of 500 N-30s and 500 N-35s.
The N-30 was similar to the N-25 except for valve and electrical system changes.
Twenty-two N-30s were converted to two-seat trainers as P-40N-31-CU. Seventy were converted to P-40R-1 trainers in 1944.
The P-40N-35-CU featured changes in the carburetor, the instruments, and the lighting. . The N-35 had modifications to the lubrication system, and featured updated electrical systems, and a new radio and ADF equipment.
As late as June 30, 1944, when the front-line equipment of all major air forces had far outpaced the potential of the P-40 series, an order for yet ANOTHER 1000 Warhawks was placed. This was the P-40N-40-CU production block. However, this order was later cut back to 220 aircraft. The N-40 was powered by the V-1710-115 engine of 1360 hp and featured metal-covered ailerons. The N-40 variant dispensed with the camouflage finish starting with 44-47860. It included improved non-metallic self-sealing fuel tanks, automatic propeller control, new radio and oxygen equipment, and flame-damping exhausts.
The last production Warhawk was a P-40N-40-CU which left the assembly line on November 30, 1944, being the 13,739th P-40 built.
One P-40N was experimentally fitted with a bubble canopy and was unofficially designated XP-40N.
The following spec refers to the P-40N-15-CU:
One 1200 hp Allison V-1710-81 twelve-cylinder liquid-cooled engine. Maximum speed 208 mph at 5000 feet, 325 mph at 10,000 feet, 343 mph at 15,000 feet. Maximum climb rate was 2120 feet per minute at 5000 feet, 2230 feet per minute at 10,000 feet. An altitude of 10,00 feet could be attained in 4.7 minutes, 20,000 feet in 8.8 minutes. Service ceiling was 31,000 feet. Range was 750 miles at 10,000 feet (clean). With one 62.4 Imp gal drop tank, range was 1080 miles. Weights were 6200 pounds empty, 8350 pounds loaded, 11,400 pounds maximum. Dimensions were wingspan 37 feet 4 inches, length 33 feet 4 inches, height 10 feet 7 inches, wing area 236 square feet.
Many of the P-40Ns were shipped to Allied air forces under Lend-Lease, and comprised the majority of the 1097 P-40s sent to the USSR. Most of their operational flying took place in the Pacific in fighter-bomber or escort roles, most of them flown by RAF, RAAF, and RNZAF pilots. In USAAF service, the P-40N was relegated largely to training roles, as later types such as the P-51 Mustang or the P-47 Thunderbolt became increasingly available in quantity.
The P-40N was known as Kittyhawk IV in RAF service. 586 P-4ONs were to be delivered to Britain, but the first 130 were diverted to the USSR. The RAF Kittyhawk IV serials were as follows:
FS270/399 (all diverted to the USSR) FT849/FT954 FX498/FX847
Although the RAF evaluated the P-40Ns in the United Kingdom, they were employed solely abroad. Most of the RAF Kittyhawk IVs were phased out of service early in 1945, but one RAF squadron continued to operate the Kittyhawk IV until the end of hostilities. RAF squadrons equipped with the P-40N included Nos 112, 250, and 450.
468 P-40Ns were sent to Australia. There serials were as follows:
P-40N-1-CU A29-415/419 A29-435/442 A29-461/472 A29-503/541 A29-559/563 A29-577/587 P-40N-5-CU A29-542/558 A29-564/576 P-40N-20-CU A29-600/704 P-40N-25-CU A29-800/811 A29-819/828 P-40N-30-CU A29-900/928 P-40N-35-CU A29-1000/1079 P-40N-40-CU A29-1100/1221
These Kittyhawk IVs were primarily operated in the South-West Pacific campaigns as low-altitude fighter and ground attack aircraft. They were progressively replaced by Mustangs and Spitfires during the last year of the war, but the Kittyhawks continued to serve with RAAF Squadrons 75, 78, and 80 until the end of hostilities.
172 P-40Ns were supplied to New Zealand. Their serials were as follows:
NZ3120/3179 NZ3182/3270 NZ3272/3293
35 P-40Ns were supplied to Canada. Their serials were 846/880.
41 P-40Ns were supplied to Brazil, where some served until 1958. They were serialled in 1945 in the range 4020/4100. One of them still survives there as a monument (USAAF serial 44-7700, Brazilian serial 4064).
An unspecified number were delivered to the Royal Netherlands East Indies Air Corps. They flew them against the Japanese in the latter stages of the war, then against the nationalist rebels in Indonesia until February of 1949.
A large proportion of the 2097 P-40s supplied to the Soviet Union were of the P-40N variety, but they were not very popular with the Russians, who considered them incapable of absorbing as much battle damage as the P-39 Airacobra.
The USAAF serials of the P-40N production blocks were as follows:
42-104429/104828 Curtiss P-40N-1-CU Warhawk c/n 38191/28590 42-104829/105928 Curtiss P-40N-5-CU Warhawk c/n 28591/29690 42-105929/106028 Curtiss P-40N-10-CU Warhawk c/n 29691/29790 42-106029/106405 Curtiss P-40N-15-CU Warhawk c/n 29791/30167 42-106406/106428 Curtiss P-40N-20-CU Warhawk c/n 30168/30190 43-22752/24251 Curtiss P-40N-20-CU Warhawk c/n 30691/32190 43-24252/24751 Curtiss P-40N-25-CU Warhawk c/n 32191/32690 44-7001/7500 Curtiss P-40N-30-CU Warhawk c/n 32741/33240 44-7501/8000 Curtiss P-40N-35-CU Warhawk c/n 33241/33740 44-47749/47968 Curtiss P-40N-40-CU Warhawk c/n 33741/33960 44-47969/48748 Curtiss P-40N-40-CU Warhawk contract cancelled.
Those few P-40Ns still in service in 1948 with the USAAF were redesignated ZF-40N.