The P-40 Warhawk was the most important fighter produced by Curtiss in World War II. It had the same basic airframe as the Curtiss P-36, but it had the more powerful, 1,100 horsepower Allison V-1710 engine - which was also used on the early Mustangs. With this power, the P-40 could fly at 375 mph.

This bird is on display at Peterson AFB, Colorado.

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Curtiss P-40 (Part 1)

By Joseph Baugher

The P-40 was the best known Curtiss-Wright airplane of World War II. It was also one of the most controversial fighters of the war. It was vilified by many as being too slow, lacking in maneuverability, 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. 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. The P-40 continued in production long after later 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.

The P-40 was 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 armor were a reflection of mid-'thirties USAAC requirements which were outmoded. The P-40 had been developed as basically a low-altitude close-support fighter under mid-1930s US tactical concepts which envisaged more need for low-level ground support operations than for high-altitude interceptions. The military doctrine of the "ascendancy of bombardment over pursuit" was dominant in 1937 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 defense and ground attack in the defense of US territory being seen as the the main tasks for any future fighter aircraft. Low-altitude performance and rugged construction received priority over high-altitude capabilities.

During the war, the Senate Special Committee to Investigate the National Defense Program (usually known as the "Truman Committee", after its chairman, Senator Harry Truman of Missouri) criticized the P-40 on several accounts, particularly on the original volume purchase of an inadequate design and its continued production long after later designs were readily available. However, they finally concluded that this was not brought about by any undue favoritism to Curtiss.

Some indication of the enormous P-40 production program undertaken by Curtiss can be assessed by its claim on factory floor space and manpower. During 1941, the Curtiss Airplane Division expanded its manufacturing area by 400 percent. The total work force was 45,000. This expansion included two new plants, one at Buffalo, New York and the other at Columbus, Ohio, to supplement the original Curtiss plant in St.Louis, Missouri. At the peak of wartime production, the entire Curtiss Airplane Division complex of factories was producing sixty aircraft A DAY!

The origin of the P-40 can be traced back to the Curtiss P-36 (Model 75) fighter, which was powered by a radial, air-cooled engine. A step in the direction toward what was eventually to emerge as the P-40 was the XP-37, which was described in an earlier post. The P-36 design was reworked to incorporate the Allison V-1710 liquid-cooled V-type engine, resulting in the XP-37. The XP-37 was equipped with a General Electrc turbosupercharger, and featured a cockpit pushed very far to the rear. Thirteen YP-37 service-test aircraft were built, but problems with the turbosupercharger caused the development of the P-37 to be abandoned in favor of a less complex and more straightforward conversion of the P-36 for the Allison V-1710 engine.

Realizing that the radial-engined P-36A was at the limit of its development, Curtiss designer Donovan Berlin got USAAC permission in July 1937 to install a 1150 hp Allison V-1710-19 liquid-cooled engine with integral supercharging in the 10th P-36A (Serial No 38-10). This project was given the company designation of Model 75P, and the USAAC gave the project a new fighter designation, XP-40.

The XP-40 flew for the first time on October 14, 1938, with Edward Elliot at the controls. Armament was two 0.50-inch machine guns located in the upper fuselage deck and synchronized to fire through the propeller arc, standard armament for US pursuit aircraft at the time. Wing racks could be fitted for six 20-pound bombs. A small oil cooler was located beneath the pointed nose. The air intake for the single-stage supercharger was mounted on top of the engine cowling between the two machine guns, but during tests it was replaced by a long cowled intake duct which became characteristic of all the early P-40 production models. Initially, the coolant radiator was placed under the fuselage aft of the wing, but it was gradually moved forward until it finally ended up located underneath the extreme nose. The radiator intake was redesigned to include an oil cooler and two coolers for the ethylene/glycol engine coolant.

The initial XP-40 had a single exhaust port on each side of the fuselage, but in its final form it had six separate exhaust ports on each side. The initial XP-40 had inherited from the P-36 a set of mainwheel fairing plates which covered the mainwheels when they retracted into their wing wells, but these were eventually deleted and replaced by two small doors which closed over the wheel struts upon retraction.

The maximum speed of the XP-40 was 342 mph at 12,200 feet at a gross weight of 6260 pounds. This was faster than the Hawker Hurricane, but slower than the Spitfire or the Bf 109E. Empty weight was 5417 pounds, and fully-loaded weight was 6870 pounds. Range was 460 miles at 299 mph with 100 gallons of fuel. With 159 gallons of fuel at 200 mph, a range of 1180 miles was claimed, almost twice that of the contemporary Hurricane, Spitfire, and Bf 109E. Wingspan was 37 feet 4 inches, wing area was 236 square feet, length was 31 feet 1 inch, and height was 12 feet 4 inches. The wingspan and wing area were to remain the same throughout the entire history of the P-40 production run.

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 planes 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 a already-proven airframe that had been been in production for some years. 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 P-40 was similar to the final XP-40 configuration except for 1040 hp V-1710-33 (C15) engines and provisions for the mounting of one 0.30-inch machine gun in each wing. Flush riveting was used to reduce drag. Armor, bulletproof windshields, and leakproof fuel tanks were added in service. The P-40 was a relatively clean design, and was unusual for the time in having a fully retractable tailwheel.

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 reached in 5.2 minutes. 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.

Foreign air forces were beginning to take notice of the P-40, and in May of 1940, the Armee de l'Air of France placed an order for 140 H-81A (export model of the P-40).

Only 200 of the initial P-40 order were actually completed as P-40s. Serials were 39-156/280 and 40-292/357. The remaining 324 aircraft of the order had their delivery deferred to enable Curtiss to expedite the delivery of the 140 H-81As to France. However, none of these actually reached France before the Armistice in June 1940, and the contract was taken over by the Royal Air Force as Tomahawk I.

16 P-40s were sent to the Soviet Union after the German invasion.

The P-40 lacked such things as armor for the pilot, self-sealing fuel tanks, and a bulletproof windshield, so it was not considered as being suitable for combat. On October 22, 1942, the P-40s still in USAAF service were ordered restricted from combat duty and were redesignated RP-40.

The P-40A designation was skipped in the initial designation assignments. However, it was applied retroactively to P-40 Ser No 40-326 when it was converted to a camera-carrying photographic reconnaissance model at Bolling Field in March of 1942.

The P-40B (Model H81B) differed from the P-40 in having an extra 0.30-inch machine gun in each wing. The engine was still the V-1710-33. In September 1940, 131 P-40Bs were procured by the Army to replace the deferred P-40s. Serials were 41-5205/5304 and 41-13297/13327. The first P-40B flew on March 13, 1941. 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 export equivalent of the P-40B was the Tomahawk IIA (Model H81-A2). They differed from the American version by having the wing guns replaced by 0.303-inch Brownings. 110 were produced for the RAF. RAF serials were AH881/990. 23 of these planes were transferred to the USSR, and one (AH938) went to Canada as an instructional airframe.

The initial P-40 order was finally completed with 193 P-40Cs (company designation H81-B). Serials were 41-13328/13520. The first flight of a P-40C was 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 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--the weights for the P-40C were 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. 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. Dimensions were wingspan 27 feet 3 1/2 inches, length 31 feet 8 1/2 inches, height 10 feet 7 inches, wing area 236 square feet.

The export equivalent of the P-40C was the Tomahawk IIB (Model H81-A2). A total of 930 were built. RAF serials were AH991/999 (all to USSR), AK100/570 (36 to China), AM370/519 (64 to China), and AN218/517.

100 of these planes, unofficially designated H81-A3, were transferred to China where they were used by the American Volunteer Group--the famous "Flying Tigers". 23 went to the USSR, and unspecified numbers went to Turkey and Egypt. The rest were used extensively by the RAF and South African Air Force in the North African theatre.

At a very early stage, the Curtiss P-40 attracted the attention of foreign air forces. On May 10, 1939, the French 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 surrendered. Britain agreed to take over the entirety of the French order, and gave the H81-A the name Tomahawk I in RAF service. RAF serials were AH741/840 and AH841/880.

The USAAC had 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 0.5-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 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.

However, Britain quickly concluded that these planes were not suitable for combat, since they lacked armor protection for the pilot, armor-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, the Hun 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. No 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 in China. AH774,793, and 840 were sold to Canada for use as instructional airframes, but they retained their RAF serials.

The Tomahawk IIA (Model H81-A2) was equivalent to the US P-40B. It had protective armor and externally-covered self-sealing tanks. 110 were built for the RAF under a direct-purchase contract. It carried two 0.30-inch machine guns in the wings in addition to the two 0.50-in guns in the fuselage. A British radio was fitted. RAF serials were AH881/990. AH938 was transferred to Canada as an instructional airframe. 23 of these planes were transferred to the USSR.

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-in 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. RAF serials were AH991/999, AK100/570 (36 of this batch were shipped to China and were selected at random with no particular sequence), AM370/519 (64 were shipped to China, selected at random), and AN218/517. They were used extensively by the RAF and the South African Air Force in North Africa starting on June 16, 1941.

After the German invasion of the USSR in June 1941, one hundred and ninety-five Tomahawk IIBs were shipped to the USSR, some from the USA, others selected from the reserve forced based in the United Kingdom in anticipation of the German invasion which never came. These Russian Tomahawks went into action on the Moscow and Leningrad fronts in October 1941, and were the first US-built planes 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 planes from both the Allies and the Axis during World War II.

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 airplane to return to base.

Although generally outclassed by the Bf 109, the Tomahawk was a capable fighter in the hands of experienced pilots such as Neville Duke. 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 (e.g. Fiat CR-42) and underpowered, lightly armed fighter monoplanes such as the Fiat G-50 of the Regia Aeronautica. It had difficulty with the more advanced Macchi C-202 Folgore.

100 of the RAF Tomahawk IIBs were released to China and served with the American Volunteer Group (AVG)--the famous "Flying Tigers". 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. There is confusion on this point.

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. General Chennault ordered 100 P-40s through a loan from the US government. By the time of Pearl Harbor, 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 Harbor. 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 bombers. When the AVG encountered the Japanese Zero for the first time, they initially underestimated the maneuverability of their opponent, and they lost two pilots on December 23. It was soon learned that it was wise not to mix it up with the Zero on a one-to-one basis because of the inferior maneuverability and climb rate of the Curtiss, but instead to use the P-40's superior speed and diving ability to advantage. The most effective tactic against the Zero was a diving pass followed by a rapid departure from the scene. The P-40 gained a reputation for ruggedness which enabled many an AVG pilot to return safely home after his plane was damaged in combat.

In May 1941, the production lines at Curtiss were busy with a new P-40 model--the P-40D. It 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.

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 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 order the P-40D into production until September of 1940, nearly 5 months after the RAF had ordered the equivalent Kittyhawk I.

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 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.

Only twenty-two P-40Ds were produced with four wing guns. US Army serial numbers were 40-359/381. An order dated February 18, 1941 increased the armament to six guns, and subsequent aircraft equipped with this armament were designated P-40E (Model 87-B2). The cannon mounts were deleted. Serial numbers of the USAAF P-40Es were 40-358, 40-382/681, 41-5305/5744, and 41-13521/13599.

The P-40E was powered by one 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), 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 4inches, length 31 feet 2 inches, height 10 feet 7 inches, and wing area 236 square feet.

The first Kittyhawk I (Model H87-A2) was flown on May 22, 1941, by which time the fighter had already been ordered by the US Army as the P-40D, the first production contract for which had been placed in September 1940. They were comparable to the US P-40D, and were fitted with four 0.50-in wing guns. Deliveries of the Kittyhawk I to the RAF began in August of 1941. After the delivery of the first twenty Kittyhawk Is, the wing-mounted armament was increased to six 0.5-inch machine guns with 281 rounds per gun. RAF serials for the Kittyhawk Is were AK571/999 and AL100/230. 72 Kittyhawk Is were diverted to Canada, the Canadian serial numbers being 1028/1099. Out of this lot, seventeen Kittyhawk Is (AK601, 636, 680, 726, 778, 882, 931, 939, 960, 971, 992, 995 and AL102, 178, 186, 188, 203) were transferred to Turkey.

The Kittyhawk IA was the RAF designation for the British equivalent of the US P-40E. Company designation was H87-A3, -A4). The designation P-40E-1 was adopted slightly in advance of the Block Designation system to identify the 1500 Kittyhawk IAs supplied to Britain early in the Lend-Lease program and to distinguish their British equipment and details from those in US service. They were virtually identical to the P-40E with the exception of British equipment such as radio installations. Since they were procured with US funds, the planes had standard Army designations and were assigned Army serial numbers. US Army serials were 41-24776/25195 and 41-35874/36953.

The RAF serial numbers were ET100/999 (equivalent US serials were 41-24776/25195 and 41-35874/36353) EV100/699 (equivalent US serials were 41-36354/36953) Many were retained for US service but retained British camouflage. Six went to Brazil. Twelve were sent to Canada in March 1942, while many others were shipped directly to Australia for use by the RAAF. Australian serials were A29-1/163. Canadian serials were 720/731. New Zealand serials were NZ3001/3044, NZ3091/3098, NZ3100/3108, and NZ3271.

Kittyhawk Is and 1As became operational with the RAF in the Western Desert on January 1, 1942. They were used against Rommel's Afrika Korps and the Italian forces in North Africa throughout the year. They were used primarily at low altitudes and for close support. The climb rate and the ceiling of the fighter were relatively poor, but, fitted with bomb racks beneath the wings from June 1942, the Kittyhawk wrought havoc among Rommel's armor. The Allison engine's poor high-altitude output limited the overall performance of the Kittyhawk to a point well below that of the Bf 109F.

A few P-40Es were converted as two seat trainers by replacing the fuselage fuel tank with a second seat.

The AVG in China had been working its P-40Cs (Tomahawk IIBs) pretty hard throughout January and February of 1942. Some were destroyed on the ground during Japanese strafing attacks, and others were lost in accidents. Cannibalization provided spares for those for those that could be kept airworthy. No more than 55 Curtiss fighters were available to the AVG at any one time. Without replacement, losses mounted rapidly and the AVG was down to some twenty P-40Cs by March of 1942. That month, thirty P-40Es were transferred to China by air from Accra in Africa. The improved performance offered by these more potent P-40s was very useful against the Zero fighters which were becoming more numerous in the Chinese theatre.

The AVG was absorbed into the USAAF as the 23rd Fighter Group on July 4, 1942. At that time, it had been officially credited with the confirmed destruction of 286 Japanese aircraft as against the loss of only 12 aircraft shot down, 8 pilots killed in action and four missing. Most of the losses were on the ground, with 61 aircraft destroyed by Japanese strafing attacks or lost in accidents. The top scoring AVG ace was Robert H. Neale, credited with 16 kills. Eight other pilots claimed ten or more victories. The Flying Tigers accounted for more victories in proportion to their numbers than any other P-40 unit.

There is a P-40E on display at the Wright-Patterson Air Force Base Museum. I am unaware of its serial number.

Sources:

War Planes of the Second World War, Fighters, Volume Four, William Green, Doubleday, 1964.

The American Fighter, Enzo Anguluci and Peter Bowers, Orion Books, 1987.

United States Military Aircraft since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.

Curtiss Aircraft, 1907-1947, Peter M. Bowers, Naval Institute Press, 1979.

The Curtiss P-40 Tomahawk, Ray Wagner, Aircraft in Profile, Volume 2, Doubleday, 1965.

The Curtiss P-40 Kittyhawk I-IV, Ray Wagner, Aircraft in Profile, Volume 6, Doubleday, 1969.

Joe Baugher

AT&T Bell Laboratories

2000 North Naperville Road

Naperville, Illinois 60566-7033