Please note: Thanks to information by Joe Baugher, an in depth historical background on the Curtiss P-40 series has been added below.
The P-40 was the best known Curtiss-Wright aircraft of World War II. It was also one of the most controversial fighters of the war. It was vilified by many at the time as being too slow, lacking in manoeuvrability, having too low a climbing rate, and being largely obsolescent by contemporary world standards even before it was placed in production. The inadequacies of the P-40 were even the subject of a Congressional investigation and it gets regularly included on lists of the worst combat aircraft of World War 2. All of these criticisms certainly had some degree of validity, but it is also true that the P-40 served its country well during the first year of the war in the Pacific when very little else was available. Along with the P-39 Airacobra, the P-40 was the only American fighter available in quantity to confront the Japanese advance during the first year of the Pacific War. It helped stem the speed of the Japanese advance until more modern types could be made available in quantity. The P-40 had no serious vices and was a pleasant aircraft to fly, and, when flown by an experienced pilot who was fully aware of its strengths and weaknesses, was able to give a good account of itself in aerial combat. Strangely enough, the P-40 continued in production long after later and more modern types were readily available, the numbers manufactured reaching the third highest total of American World War II fighters, after the Republic P-47 and the North American P-51. In hindsight, many of the criticisms levelled at the P-40 can be attributed to the aircraft being used in roles it was not initially designed for.
The P-40 was already obsolete by European standards even before the first prototype flew, and it never did catch up. Its initial inadequacies, in the form of low firepower and lack of self-sealing fuel tanks or armour, were a reflection of mid-thirties USAAC requirements. The P-40 had been developed basically as a low altitude close support fighter under US tactical concepts which envisaged more need for low-level ground support operations than for high altitude interceptions. Low altitude performance and rugged construction received priority over high altitude capabilities. The military doctrine of the "ascendancy of bombardment over pursuit" was dominant in 1939 when the P-40 first appeared. This doctrine assumed that the prospect of high altitude enemy air attack on the USA was extremely remote, with coastal defence and ground attack in the defence of US territory being seen as the main tasks for any future fighter aircraft.
In the late 1930s, the USAAC was planning to expand its force, and on January 25, 1939 manufacturers were invited to submit proposals for pursuit aircraft. The Army was still thinking in terms of low altitude, short range fighters. Among the contenders were the Lockheed XP-38, the Bell XP-39, the Seversky/Republic XP-41 (AP-2) and XP-43 (AP-4), and no less than three aircraft from Curtiss, the H75R, XP-37, and XP-42. Although the XP-40 could not match the performance (especially at altitude) of the turbosupercharged types, it was less expensive and could reach quantity production fully a year ahead of the other machines. In addition, the XP-40 was based on the already proven radial engined Hawk 75 (P-36) that had been in production since 1935. Consequently, on April 26, 1939, the Army adopted a conservative approach and ordered 524 production versions under the designation P-40 (Curtiss Model 81). At that time, it was the largest ever production order for a US fighter, and dwarfed the service test orders placed that same day for YP-38 and YP-39 fighters. A couple of weeks later, 13 YP-43s were also ordered.
The production P-40 was similar to the final XP-40 configuration except for the use of a 1040 hp V-1710-33 (C15) engine. The armament was the standard USAAC armament of the day, two 0.50 inch machine guns, mounted in the upper nose and synchronized to fire through the propeller arc. Provisions were made for the mounting of one 0.30 inch machine gun in each wing. Flush riveting was used to reduce drag. Armour, bullet-proof windshields, and leak-proof fuel tanks were not initially fitted and were later added to the aircraft while it was in in service. The P-40 was a relatively clean design, and was unusual for the time in having a fully retractable tail-wheel.
The first flight of a P-40 (Ser No 39-156) was on April 4, 1940. Maximum speed was 357 mph at 15,000 feet, service ceiling was 32,750 feet, and initial climb rate was 3080 feet per minute. An altitude of 15,000 feet could be reached in 5.2 minutes. Cruising speed was 272 mph, landing speed was 80 mph, and the range at 250 mph was 950 miles. The length of the P-40 was 31 feet 8 3/4 inches, which became standard for all early models. Weights were 5376 pounds empty, 6787 pounds gross, and 7215 pounds maximum.
Deliveries of the P-40 to Army units began in June of 1940. Three of the P-40s were used for service testing, the USAAC contract making no provisions for the standard practice of supplying YP models. They were delivered with full camouflage applied, olive drab on the top and grey on the undersides. The standard rudder stripes and star insignia were applied to both wings. The first USAAC units to operate the P-40 were the 33rd, 35th and 36th Pursuit Squadrons of the 8th Pursuit Group, based at Langley Field, Virginia. It was soon followed by the 55th, 77th, and 79th Pursuit squadrons of the 20th Pursuit Group at Selfridge Field, Michigan, and the 21th, 34th, and 70th Pursuit Squadrons of the 35th Pursuit group which trained on P-40s prior to being issued with P-39s.
At a very early stage, the Curtiss P-40 attracted the attention of foreign air forces. On May 10, 1939, the French government ordered 140 export versions of the P-40 for the Armee de l'Air. These aircraft were designated Hawk 81-A1 by the manufacturer. The Hawk 81-A1s were identical to the US P-40 except that they had French instruments and equipment and were equipped with reverse-movement "French-fashion" throttles. The first of the French ordered H81-A1s flew on June 6, 1940, and a few were actually completed with French markings. However, before any of their H81-A1s could be delivered, France had surrendered. Britain agreed to take over the entirety of the French order, and gave the H81-A the name Tomahawk I in RAF service. In September of 1940, the USAAC agreed to defer deliveries of their P-40s so that the Tomahawk Is could be supplied to Britain as soon as possible. The first Tomahawk Is reached England in September of 1940. The two 0.50 inch machine guns in the nose were retained, but they were supplemented by four wing-mounted 0.303 inch Browning machine guns in place of the 7.5 mm FN-Brownings originally specified by the French. Such was the urgency of their delivery to Britain that many of the 140 machines still had French instruments and bore cockpit lettering in French when they arrived.
The RAF quickly concluded that these aircraft were not suitable for combat, since they lacked armour protection for the pilot, armour-glass windshields, or self-sealing fuel tanks. Nevertheless, since a German invasion was feared to be imminent, they were actually issued to several operational squadrons. However, Germany never invaded England, and so the Tomahawk Is were used only for training roles within Britain. Overseas, the first Desert Air Force squadron to be equipped with Tomahawks was No. 112 which exchanged its Gloster Gladiators for the Curtiss fighter. 112 Squadron became famous for its "shark's tooth" insignia on the engine cowling, and this scheme was later adopted by the American Volunteer Group (AVG) in China. For much the same reasons as as the RAF, P-40s still in USAAF service were ordered restricted from combat duty on October 22, 1942 and were redesignated RP-40.
Meanwhile, the deferred deliveries of the P-40 to the USAAC were picked up again with the P-40B (The P-40A designation was skipped in the initial designation assignments). In September 1940, 131 P-40Bs were procured by the Army to replace the deferred P-40s The P-40B (Model H81-B) differed from the P-40 in having an extra 0.30 inch machine gun in each wing, bringing the total to four. The two 0.50 inch guns in the fuselage were retained. The engine was still the V-1710-33. The first P-40B flew on March 13, 1941 and the aircraft were delivered in full camouflage. In contrast to the earlier P-40, the tail stripes and upper right and lower port wing stars were no longer present, but a star now appeared on each side of the fuselage. The P-40B retained the same dimensions of the P-40, but weight was increased to 5590 pounds empty, 7326 pounds gross, and 7600 pounds maximum loaded. Because of the additional weight, the P-40B had an inferior performance to the P-40, maximum speed being 352 mph, service ceiling being 32,400 feet, and initial climb rate being 2860 feet per minute. Normal range was 730 miles, but a maximum range of 1230 miles could be attained at the minimum cruise settings.
The initial USAAC P-40 order was finally completed with 193 P-40Cs (company designation H81-B). With the first flight of a P-40C being made on April 10, 1941. The P-40C retained the 1150 hp Allison V-1710-33 engine, but was fitted with a new fuel system with 134 gallons in new tanks with improved self sealing. In addition, provisions were made for a 52 gallon drop tank carried below the fuselage. The P-40C had a SCR-247N radio instead of the SCR-283. These additions produced yet another upward crawl in the weight of the aircraft with the weights for the P-40C being 5812 pounds empty, 7459 pounds gross, and 8058 pounds maximum loaded. Consequently, the performance continued to degrade, maximum speed was 345 mph at 15,000 feet and normal and maximum ranges were 730 and 945 miles respectively. Service ceiling was 29,500 feet, and initial climb rate was 2650 feet per minute. During 1941, a substantial number of P-40Bs and Cs were shipped to USAAC bases overseas, including the 15th and 18th Pursuit Groups at Wheeler Field, Hawaii and the 20th Pursuit Squadron of the 24th Pursuit Group at Clark Field in the Philippines. In addition, a dozen P-40Cs had been delivered to the 18th Pursuit Group's 44th Pursuit Squadron at Bellows Field, Hawaii. Over 60 P-40Cs were destroyed on the ground at Wheeler during the Pearl Harbour attack on December 7, 1941. Only a few were able to get airborne, and were quickly shot down by Zeros. A few others from Haleiwa airfield and four aircraft from the 47th Pursuit Group managed to make some attacks on the Japanese formation, claiming 5 kills. However, at the end of the Pearl Harbour attack, only 25 P-40s remained airworthy. A similar scenario took place in he Philippines, where many P-40s were destroyed on the ground.
Tomahawk II was the designation given to a new and improved export P-40, one which was better equipped for combat. It was functionally equivalent to the P-40B and P-40C then being issued to USAAC units. Unfortunately, some discrepancies exist in Curtiss records matching Tomahawk designations to RAF serial numbers and correlation to P-40s. The Tomahawk IIA (Model H81-A2) was equivalent to the US P-40B. It had protective armour and externally covered self-sealing tanks. Armament was two 0.30 inch machine guns in the wings in addition to the two 0.50 inch guns in the fuselage and a British radio was fitted. 110 were built for the RAF under a direct purchase contract. Tomahawk IIA AH938 was transferred to Canada as an instructional airframe and AH936, 952, 965/971, 974/895, 987, 989, and 990 were delivered to the Soviet Union.
The Tomahawk IIB (Model H81-A2) was generally equivalent to the US P-40C. It had four 0.303 inch Browning machine guns in the wings in addition to the two nose-mounted 0.50 inch guns. Whereas the Tomahawk IIA had a British radio, the Tomahawk IIB had US equipment. A total of 930 of these planes were produced in four lots (31 were lost at sea in transit). After the German invasion of the USSR in June 1941, 195 Tomahawk IIBs were shipped to the USSR. Some were shipped directly from the USA while others were selected from the reserve force based in the Britain in anticipation of the German invasion which never came. The Russian Tomahawks went into action on the Moscow and Leningrad fronts in October 1941, and were the first US built aircraft to be used by the Russians in the new battle area. An unspecified number of Tomahawk IIBs were sent to bolster Turkish neutrality in November 1941 (Turkey was supplied with aircraft from both the Allies and the Axis during World War 2) and a further 6 were transferred from the RAF to the Royal Egyptian Air Force.
The Tomahawk IIs were active in the Middle East from October of 1941 onward. They shared in the strafing of the retreating Axis troops. The ability of the Tomahawk to absorb an incredible amount of punishment became almost legendary. They served with Nos. 2, 26, 73, 112, 136, 168, 239, 241, 250, 403, 414, 430 and 616 Squadrons of the RAF. They also served with Nos. 2 and 4 Squadrons of the South African Air Force and No 3 Squadron of the Royal Australian Air Force. At low altitudes, the Tomahawk II was actually superior to the Bf-109, but this advantage rapidly disappeared when combat took place at altitudes above 15,000 feet. The weight which handicapped the performance of the Tomahawk did have one tangible benefit, the rugged structure could absorb a terrific amount of battle damage and still allow the aircraft to return to base. Although generally outclassed by the Bf 109, the Tomahawk was a capable fighter in the hands of experienced pilots. Wing Commander Clive Caldwell of the RAAF scored more than twenty victories while flying a Tomahawk in the Middle East. However, much of the opposition to the Tomahawk was provided by obsolescent fighter biplanes like the Fiat CR-42 and under powered, lightly armed fighter monoplanes such as the Fiat G-50 of the Regia Aeronautica. The more advanced Macchi C-202 Folgore proved more of a handful for the Tomahawk.
During 1941, 100 RAF Tomahawk IIBs were released and diverted to China and served with the American Volunteer Group (AVG), the famous "Flying Tigers". Curtiss company records list them as Model H81-A3. The Tomahawk IIB was more or less equivalent to the P-40C, but some sources list the Flying Tiger Tomahawks as being equivalent to the P-40B. As previously mentioned, there are some discrepancies between Curtiss records matching Tomahawk designations to RAF serials and to equivalent US Army P-40 models, so there is confusion on this point. Erik Shilling, who was a member of the AVG and who was also a flight leader and an engineering officer for the group, maintains that the aircraft with the AVG were actually export models of the P-40B and not the C (after all, he was there and he ought to know). He says that the aircraft did not have the equipment to carry the external 52 gallon drop tank, nor were they equipped with bomb shackles. In addition all of the fuel tanks had external self-sealing material, not internally mounted sealing material as in the "C" model. Also the Model "C" had armour plate in the front, ahead of the pilot, installed on the firewall between the two 50 calibre's, the AVG's planes did not. It is with the Flying Tigers that the P-40 achieved immortality. Newly promoted to Brigadier General in the Chinese Army, Claire Chennault went to the USA in November 1940 to recruit pilots for the AVG. The AVG came into existence in August 1941, and was backed by the US government in recognition of China's fight against the invading Japanese. General Chennault ordered 100 P-40s through a loan from the US government. The Tomahawk IIBs were shipped to Rangoon, Burma, arriving in June of 1941. They were reassembled there and were flown to the AVG base at Toungoo, Burma, where they were intended to defend the Burma Road between Chungking and Lashio. After Pearl Harbour, the AVG moved to Kunming. By the time of Pearl Harbour, some 80 American pilots were serving with the AVG based at Kunming and Mingaladon. Contrary to popular understanding, the AVG did not actually enter combat until after Pearl Harbour. The famous "shark's teeth" marking did not originate with the Flying Tigers, but was copied from the markings used by the Tomahawks of the RAF's No. 112 Squadron in North Africa.
The AVG drew first blood on December 20, destroying six out of ten attacking Japanese Ki 21 bombers. When the AVG encountered Japanese fighters for the first time, they initially underestimated the manoeuvrability of their opponents, and they lost two pilots on December 23. It was soon learned that it was wise not to mix it up with Japanese fighters on a one to one basis because of the inferior manoeuvrability and climb rate of the Curtiss, but instead to use the P-40's superior speed and diving ability to maximum advantage. The most effective tactic against the Japanese was found to be a diving pass followed by a rapid exit from the scene. The Tomahawk gained a reputation for ruggedness which enabled many an AVG pilot to return safely home after his plane was damaged in combat. However, the stress of combat and lack of spares had taken their toll, and by March of 1942, only 20 Curtiss machines were serviceable so 30 P-40Es were issued to the AVG. By the time that the AVG was incorporated as the 23rd Fighter Group of the USAAF in July 1942, the AVG pilots had clamed 286 confirmed kills, with four Curtiss machines having been lost in combat. However a lot more had been lost in Japanese strafing attacks and many had to be cannibalized to keep others in the air.
Contrary to popular myth, the AVG Tomahawks never encountered the Japanese A6M Zero-sen in combat. At that stage in the war, all the Zeros had been moved out of China and eastward into the Pacific or southward to the Netherlands East Indies. The fighter that the Tomahawks actually encountered was the Japanese army fighter, the Nakajima Ki 43 Hayabusa (code named Oscar). However, at that stage of the war, virtually every Japanese single-seat fighter was called a "Zero"
Also during 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, the Model 87. The P-40D introduced a new shorter nose design that was retained by all subsequent P-40s. The 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, 175 pounds of armour was 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 87-A1 by the company, but this designation was cancelled after France fell. 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. Only twenty two P-40Ds were produced. An order dated February 18, 1941 increased the armament to six guns in the wings, and subsequent aircraft equipped with this armament were designated P-40E (Model 87-B2). The cannon mounts (which were never used in any case) were deleted.
The P-40E was powered by a 1150 hp Allison V-1710-39 twelve cylinder Vee liquid cooled engine. Maximum speed was 335 mph at 5000 feet, 345 mph at 10,000 feet, and 362 mph at 15,000 feet. Initial climb rate was 2100 feet per minute. An altitude of 20,000 feet could be attained in 11.5 minutes. Service ceiling was 29,000 feet. Maximum range was 650 miles clean, 850 miles with one 43 Imp gal drop tank and 1400 miles with one 141.5 Imp gal drop tank. Weights were 6350 pounds empty, 8280 pounds normal loaded, and 9200 pounds maximum. Dimensions were wingspan 27 feet 4 inches, length 31 feet 2 inches and height 10 feet 7 inches.
The Kittyhawk IA was essentially the export equivalent of the P-40E. 1500 were built, primarily for the RAF, but many were diverted to Canada, Australia, and New Zealand. Following the passage of the Lend-Lease Act, all aircraft purchased with US funds had to have standard US designations and had to be issued USAAF serial numbers, even though they were never intended for service with the USAAF. Since the Kittyhawk IA was built with some British equipment, it was not exactly equivalent to the USAAF P-40E, and the Kittyhawk IA was assigned the US designation P-40E-1 (Model 87A-4) to recognize the difference.
In 1941, P-40D Ser No 40-360 was fitted with a 1300 hp British built Rolls-Royce Merlin 28 engine with a single-stage two-speed supercharger. It flew for the first time on June 30, 1941. This experimental P-40D could be distinguished from the stock P-40E by the absence of the top-mounted carburettor air scoop. The Merlin engine did much to overcome the limitations imposed by the Allison and a total of 1311 examples powered by the American made version of the Merlin built by the Packard Motor Car Company were ordered under the designation P-40F. The P-40F and later versions were known by the name "Warhawk" in US service. The P-40F was powered by a Packard built Merlin V-1650-1 twelve cylinder Vee liquid-cooled engine rated at 1300 hp for takeoff and 1120 hp at 18,500 feet. Maximum speed was 320 mph at 5000 feet, 340 mph at 10,000 feet, 352 mph at 15,000 feet and 364 mph at 10,000 feet. An altitude of 10,000 feet could be attained in 4.5 minutes, and an altitude of 20,000 feet could be reached in 11.6 minutes. Maximum range was 700 miles at 20,000 feet (clean), 875 miles with one 43 Imp gal drop tank and 1500 miles with a 141.5 Imp gal drop tank. Service ceiling was 34,400 feet. Weights were 6590 pounds empty, 8500 pounds normal loaded and 9350 pounds maximum. Dimensions were 37 feet 4 inches wingspan, 33 feet 4 inches length (P-40F-5-CU and later) and 10 feet 7 inches high. Armament consisted of six 0.50 in machine guns in the wings.
The first 699 planes of the P-40F series had no dash numbers, since the production block designation system was not yet in effect. The dash numbers were first used with the P-40F-5-CU model, which introduced a fuselage elongated from 31 feet 2 inches to 33 feet 4 inches in order to improve directional stability. This longer fuselage was retained in all later P-40 versions. The P-40F-10-CUs had manual instead of electrically operated cowl flap controls. The P-40F-15-CUs had winterizing equipment, and the P-40F-20-CUs had a revised oxygen flow system for the pilot. A radio mast was fitted to late production P-40Fs. One hundred and fifty P-40Fs were supplied to the RAF under Lend-Lease. The RAF assigned them the name Kittyhawk II although very few of these aircraft actually served with the RAF. A number were lost at sea before reaching the RAF while others were returned to the USAAF and the Free French for use in North Africa in 1942/43. A further 100 were transferred to the USSR.
The designation YP-40F was unofficially assigned to P-40F Ser No 41-13602 used for experimental tests of the cooling system and the tail rudder. The coolant system was moved aft in several different configurations, including a mounting fitted inside a thickened wing-root section. A number of P-40Fs were selected at random, withdrawn from operational service, and fitted with Allison V-1610-81 in place of their original Merlins. These aircraft were intended for training duties and were redesignated P-40R-1. Similar conversions from the P-40L were designated P-40R-2. Army records report that over 600 such conversions were made, but only 70 such conversions can be confirmed by serial number
The designation P-40G was given to 44 existing Army P-40s that were fitted with H81-A2 Tomahawk IIA wings that carried four 0.30 inch machine guns. The first such conversion was P-40 39-221, which was assigned the unofficial designation XP-40G. The remaining 43 retrofits took place between August and September 1941. Company records refer to these conversions under the designation Model 81-AG. Sixteen of these P-40Gs were shipped to the USSR starting in October 1941. All those examples remaining in the USA were redesignated RP-40G in October 1942, where the R meant "restricted from combat use".
For some reason, the designation P-40H was never assigned. Likewise, the designation P-40I was never assigned in case the letter "I" was confused with the number 1. The designation P-40J was given to a projected version of the P-40E which was to have a turbosupercharged engine. This study was abandoned in May 1942 without anything ever being built.
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.
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 IIIs, the first examples were delivered to the Middle East in late 1942. Forty two P-40Ks served with the RAAF, 25 P-40Ks were diverted to Brazil and a further 9 P-40K-1-CUs served with the RCAF. P-40Ks serving with the RNZAF were NZ3045/3065, NZ3090, and NZ3099.
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 centre section and a slim, pointed nose.
In order to improve the Merlin powered Warhawk's performance in short range combat, the P-40L version was created. The P-40L (Model 87-B3) was basically a "stripped" version of the Merlin powered P-40F-5-CU, in which 250 pounds of weight was saved by the partial removal of fuel, armament, and other equipment. The P-40L was otherwise virtually identical to the Merlin powered P-40F-5-CU. Some of the P-40L production blocks featured aircraft with reduced armament and smaller capacity fuel tanks in order to obtain even more reduced weight and even better performance. The L model was sometimes known as the "Gipsy Rose Lee", after the famous strip-tease dancer of the time. While the P-40L-1-CU had the same fuel and armament as the P-40F, the P-40L-5-CU and subsequent P-40Ls had two of their wing guns removed to reduce the total armament to four 0.50 inch machine guns with 201 rounds per gun. Internal fuel was reduced by 31 Imp gal by the removal of front wing tanks. Other changes included electrical aileron trim tabs and engine control changes (P-40L-10-CU), revised carburettor air filters and inter-aircraft signal lights (P-40L-15-CU) and radio and electrical changes and provisions for an incendiary (destruct) grenade (P-40L-20-CU). Despite the weight savings, the maximum speed of the P-40L was a mere 4 mph greater than that of the P-40F at rated altitude. One hundred P-40Ls were sent to Britain as Kittyhawk IIs with no mark distinctions from the P-40Fs. 160 other P-40Ls reached the RAF as Kittyhawk IIIs.
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. Other detail changes on the P-40M included reinforced ailerons (P-40M-1-CU), improved carburettor air filters and further aileron improvements (P-40M-5-CU) and revised undercarriage warning systems and fuel system changes (P-40M-10-CU). 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 and the majority of them went to the RAF and the RAAF as the Kittyhawk III. 34 P-40Ms went to New Zealand as serial numbers NZ3066/3073, NZ3075/3089, NZ3109/3119, and NZ3180. The type served with British Commonwealth forces in the Far East and number were operated in Italy by No. 5 Squadron of the South African Air Force. A further 19 P-40Ms were transferred to Brazil.
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 (as previously mentioned) shortages of the Packard built Merlin caused this order to be cancelled and the P-40N with the 1360 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 armour was reintroduced, and aluminium 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 with 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. Under-wing 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-5s 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 while the P-40N-35-CU featured changes in the carburettor, the instruments, and the lighting. The N-35 also had modifications to the lubrication system, featured updated electrical systems and a new radio and ADF equipment. 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.
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 and 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).
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. Much 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-40Ns were to be delivered to Britain, but the first 130 were diverted to the USSR. 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 supplied to Australia, 172 were supplied to New Zealand (NZ3120/3179, NZ3182/3270, NZ3272/3293), 35 were supplied to Canada and 41 were supplied to Brazil, where some served until 1958. 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. Those few P-40Ns still in service in 1948 with the USAAF were redesignated ZF-40N.
The P-40Q was an experimental project which attempted to produce a really modern fighter out of the existing P-40. The modifications were in fact so drastic that there was very little in common with earlier P-40 versions. Two P-40Ks (serial numbers 42-9987 and 42-45722) and one P-40N (serial number 43-24571) were extensively modified with revised cooling systems, two-stage superchargers, and structural changes which markedly altered their appearance. The project was assigned the designation XP-40Q. The first XP-40Q was P-40K-10-CU serial no. 42-9987 fitted with a new cooling system, a longer nose, and a four-bladed propeller. The radiators were moved into an under fuselage position, with intakes between the undercarriage legs. The most prominent XP-40Q feature, used on 42-45722 and 43-24571, was the cutting down of the rear fuselage and the addition of a bubble canopy as on the "XP-40N". Later the wingtips were clipped. The result was an aircraft which bore almost no resemblance whatsoever to its parent P-40 line. The V-1710-121 engine was fitted with water injection, resulting in a power of 1425 hp. Speed increased to 422 mph at 20,500 feet, making it the fastest of all the P-40s. An altitude of 20,000 feet could be reached in 4.8 minutes, and service ceiling was 39,000 feet. Four 0.50 inch machine guns were carried by the prototypes. Wingspan was 35 feet 3 inches (after clipping), and length was 35 feet 4 inches (2 feet longer than the P-40N).
The proposed production models of the P-40Q were to have carried either six 0.50 inch machine guns or four 20 mm cannon, but the XP-40Q was still inferior to contemporary production Mustangs and Thunderbolts so development was therefore abandoned. Consequently, the production life of the P-40 ended with the N version. The second XP-40Q was briefly used for post-war air racing. Registered NX300B, it was an unauthorized starter in the 1947 Thompson Trophy race and was in fourth place when it caught fire and had to drop out of the race.
The designation P-40R was assigned to P-40F and P-40L airframes that had their Packard Merlin engines replaced in service with Allison V-1710-81 engines. Converted P-40Fs were redesignated P-40R-1, converted P-40Ls as P-40R-2. These planes were used exclusively for training duties.
The RNZAF received it's first 44 ex-RAF P-40Es in mid 1942 to replace aircraft such as the Harvard and Hawker Hind. A total of 297 P-40E (Kittyhawk IA - NZ3001/3044, NZ3091/3098, NZ3100/3108, NZ3271), P-40K (Kittyhawk III - NZ3045/3065, NZ3090, NZ3099), P-40L (Kittyhawk II - NZ3074), P-40M (Kittyhawk III - NZ3066/3073, NZ3075/3989, NZ3109/3119, NZ3180) and P-40Ns (Kittyhawk IV - NZ3120/3179, NZ3181/3270,NZ3272/3293) were in use between 1942 and 1945 with a further 4 being destroyed in accidents before becoming operational. The aircraft were assigned to Nos. 14, 15, 16, 17, 18, 19 and 20 Fighter Squadrons, and No's 2 and 4 (F) OTU (Operational Training Unit).
Number 14 through 19 Squadrons were deployed to the Pacific theatre in 1943, where they carried out offensive and defensive fighter operations, dive bombing duties and bomber escort. RNZAF P-40's accounted for 99 Japanese aircraft destroyed and 14 probables for the loss of 20 to enemy action. A further 76 were written off in crashes overseas and 76 in crashes in New Zealand. The P-40 began to be replaced in front line duties by F4U-1A Corsairs from 1944 and, like so many aircraft of this era, most of the surviving RNZAF P-40s were sold for scrap in 1948 with only 6 surviving destruction.
The P-40 pictured here (USAAF issue no. 42-104730, RAAF serial no. A29-448, GA-C) is a former 75 squadron, RAAF P-40N-1-CU. Out of a total of only 400 P-40N-1s built, 70 saw service with the RAAF and this particular aircraft is the only remaining airworthy model. A29-448 spent its active career in New Guinea with 75 Squadron, although for its final few missions it was assigned to 78 squadron, RAAF. In May 1944 the aircraft was damaged in a forced landing at Tadji field, Aitape, New Guinea and was disassembled before being placed in open storage there along with several other damaged RAAF aircraft.
In 1974 a team consisting of mainly Australians and New Zealanders went to Tadji with the task of locating and shipping dozens of aircraft remains to the United States. As a result, several team members were able to acquire aircraft for themselves and A29-448 ended up in New Zealand in the hands of Charles Darby. One aspect of the aircraft which remains a mystery was the discovery of a second RAAF serial number on the starboard fuselage. While A29-448 corresponds to the USAAF number 42-104730 and is correct for a P-40N-1-CU, the second number (A29-1050) is from a P-40N-35-CU. This dual identity was also noticed on four other P-40s found nearby.
On arrival in New Zealand the aircraft was placed into storage for many years while parts were sourced to help in its restoration. In April 1997 Charles Darby entered into an ownership partnership with Garth Hogan to restore A29-448 to an airworthy condition. Work commenced on restoration at Pacific Aircraft Ltd and when that company ceased trading in June 1997, Garth took over the lease and formed Pioneer Aero Restorations and work continued on the aircraft at the East Tamaki facility. During restoration a second seat was installed behind the pilot. In order to keep the aircraft authentic, removable rear panels were installed so that when the seat is not in use the aircraft quickly reverts to stock standard condition. Another variation from the original was the use of P-40E wings (which were fitted with six guns). This did not prove to be a problem as, although the P-40N left the factory with an armament of four 0.50 inch guns, the aircraft were able to take a further two so most were reverted to six gun configuration. On March 17, 2000 (after final assembly and testing at RNZAF base Hobsonville) A29-448, now registered as ZK-CAG, flew for the first time in almost 56 years.
Power Plant: One 1,013kW (1,360hp) Allison V-1710-81
Wingspan: 11.38m (37ft 3 1/2in)
Length: 10.16m (33ft 3 3/4in)
Max T-O weight: 4,014kg (8,850lb)
Max Level speed: 608km/h (378mph)
Range: 386km (240miles)