The Curtiss P-40 Warhawk is an American single-engined, single-seat, all-metal fighter and ground-attack aircraft that first flew in 1938. The P-40 design was a modification of the previous Curtiss P-36 Hawk which reduced development time and enabled a rapid entry into production and operational service. The Warhawk was used by most Allied powers during World War II, and remained in frontline service until the end of the war. It was the third most-produced American fighter of World War II, after the P-51 and P-47; by November 1944, when production of the P-40 ceased, 13,738 had been built, all at Curtiss-Wright Corporation's main production facilities at Buffalo, New York.
P-40 Warhawk was the name the United States Army Air Corps gave the plane, and after June 1941, USAAF adopted the name for all models, making it the official name in the U.S. for all P-40s. The British Commonwealth and Soviet air forces used the name Tomahawk for models equivalent to the P-40B and P-40C, and the name Kittyhawk for models equivalent to the P-40D and all later variants.
P-40s first saw combat with the British Commonwealth squadrons of the Desert Air Force in the Middle East and North African campaigns, during June 1941. No. 112 Squadron Royal Air Force, was among the first to operate Tomahawks in North Africa and the unit was the first Allied military aviation unit to feature the "shark mouth" logo, copying similar markings on some Luftwaffe Messerschmitt Bf 110 twin-engine fighters.
The P-40's lack of a two-speed supercharger made it inferior to Luftwaffe fighters such as the Messerschmitt Bf 109 or the Focke-Wulf Fw 190 in high-altitude combat and it was rarely used in operations in Northwest Europe. However, between 1941 and 1944, the P-40 played a critical role with Allied air forces in three major theaters: North Africa, the Southwest Pacific, and China. It also had a significant role in the Middle East, Southeast Asia, Eastern Europe, Alaska and Italy. The P-40's performance at high altitudes was not as important in those theaters, where it served as an air superiority fighter, bomber escort and fighter-bomber. Although it gained a postwar reputation as a mediocre design, suitable only for close air support, more recent research including scrutiny of the records of individual Allied squadrons indicates that this was not the case: the P-40 performed surprisingly well as an air superiority fighter, at times suffering severe losses, but also inflicting a very heavy toll on enemy aircraft. Based on war-time victory claims, over 200 Allied fighter pilots from 7 different nations (United Kingdom, Australia, New Zealand, Canada, South Africa, the United States, and the Soviet Union) became aces flying the P-40, with at least 20 double aces mostly in the North Africa, China-Burma-India, Pacific and Russian Front theaters. The P-40 offered the additional advantage of low cost, which kept it in production as a ground-attack aircraft long after it was obsolete as a fighter.
Development and production
On 14 October 1938, Curtiss test pilot Edward Elliott flew the prototype XP-40 on its first flight in Buffalo. The XP-40 was the 10th production Curtiss P-36 Hawk, with itsPratt & Whitney R-1830 Twin Wasp 14-cylinder air-cooled radial engine replaced at the direction of Chief Engineer Don R. Berlin by a liquid-cooled, supercharged Allison V-1710 V-12 engine. The first prototype placed the glycol coolant radiator in an underbelly position on the fighter, just aft of the wing's trailing edge. USAAC Fighter Projects Officer Lieutenant Benjamin S. Kelsey flew this prototype some 300 miles in 57 minutes, approximately 315 miles per hour (507 km/h). Hiding his disappointment, he told reporters that future versions would likely go 100 miles per hour (160 km/h) faster. Kelsey was interested in the Allison engine because it was sturdy and dependable, and it had a smooth, predictable power curve. The V-12 engine offered as much power as a radial engine but had a smaller frontal area and allowed a more streamlined cowl than an aircraft with a radial engine, promising a theoretical 5% increase in top speed.
Curtiss engineers worked to improve the XP-40's speed by moving the radiator forward in steps. Seeing little gain, Kelsey ordered the aircraft to be evaluated in a NACA wind tunnel to identify solutions for better aerodynamic qualities. From 28 March to 11 April 1939, the prototype was studied by NACA. Based on the data obtained, Curtiss moved the glycol coolant radiator forward to the chin; its new air scoop also accommodated the oil cooler air intake. Other improvements to the landing gear doors and the exhaust manifold combined to give performance that was satisfactory to the USAAC. Without beneficial tail winds, Kelsey flew the XP-40 from Wright Field back to Curtiss's plant in Buffalo at an average speed of 354 mph (570 km/h).[N 2] Further tests in December 1939 proved the fighter could reach 366 mph (589 km/h).
An unusual production feature was a special truck rig to speed delivery at the main Curtiss plant in Buffalo, New York. The rig moved the newly built P-40s in two main components, the main wing and the fuselage, the eight miles from the plant to the airport where the two units were mated for flight and delivery.
The P-40 was conceived as a pursuit aircraft and was agile at low and medium altitudes but suffered from a lack of power at higher altitudes. At medium and high speeds it was one of the tightest-turning early monoplane designs of the war, and it could out turn most opponents it faced in North Africa and the Russian Front. In the Pacific Theater it was out-turned at lower speeds by the lightweight fighters A6M Zero and Nakajima Ki-43 "Oscar" which lacked the P-40's structural strength for high-speed hard turns. The American Volunteer Group Commander Claire Chennault advised against prolonged dog-fighting with the Japanese fighters due to speed reduction favouring the Japanese.
Allison's V-1710 engines produced 1,040 hp (780 kW) at sea level and 14,000 ft (4,300 m). This was not powerful compared with contemporary fighters, and the early P-40 variants' top speeds were only average. The single-stage, single-speed supercharger meant that the P-40 was a poor high-altitude fighter. Later versions, with 1,200 hp (890 kW) Allisons or more powerful 1,400 hp Packard Merlin engines were more capable. Climb performance was fair to poor, depending on the subtype. Dive acceleration was good and dive speed was excellent. The highest-scoring P-40 ace, Clive Caldwell (RAAF), who claimed 22 of his 28½ kills in the type, said that the P-40 had "almost no vices", although "it was a little difficult to control in terminal velocity". The P-40 had one of the fastest maximum dive speeds of any fighter of the early war period, and good high-speed handling.
Evidence of the P-40's durability: in 1944 F/O T. R. Jacklin (pictured) flew this No. 75 Squadron RAAF P-40N-5 more than 200 mi (322 km) after the loss of the port aileron and 25% of its wing area, due to a mid-air collision with another P-40N-5.
The P-40 tolerated harsh conditions and a variety of climates. Its semi-modular design was easy to maintain in the field. It lacked innovations such as boosted ailerons or automatic leading edge slats, but its strong structure included a five-spar wing, which enabled P-40s to pull high-G turns and survive some midair collisions. Intentional ramming attacks against enemy aircraft were occasionally recorded as victories by the Desert Air Force and Soviet Air Forces. Caldwell said P-40s "would take a tremendous amount of punishment, violent aerobatics as well as enemy action". Operational range was good by early war standards and was almost double that of the Supermarine Spitfire orMesserschmitt Bf 109, although inferior to the Mitsubishi A6M Zero, Nakajima Ki-43 and Lockheed P-38 Lightning.
Caldwell found the P-40C Tomahawk's armament of two .50 in (12.7 mm) Browning AN/M2 "light-barrel" dorsal nose-mount synchronized machine guns and two .303 Browning machine guns in each wing to be inadequate. This was improved with the P-40D (Kittyhawk I) which abandoned the synchronized gun mounts and instead had two .50 in (12.7 mm) guns in each wing, although Caldwell still preferred the earlier Tomahawk in other respects. The D had armor around the engine and the cockpit, which enabled it to withstand considerable damage. This allowed Allied pilots in Asia and the Pacific to attack Japanese fighters head on, rather than try to out-turn and out-climb their opponents. Late-model P-40s were well armored. Visibility was adequate, although hampered by a complex windscreen frame, and completely blocked to the rear in early models by a raised turtledeck. Poor ground visibility and relatively narrow landing gear track caused many losses on the ground.
Curtiss tested a follow-on design, the Curtiss XP-46, but it offered little improvement over newer P-40 models and was cancelled.
Operational history : British and Commonwealth
In all, 18 Royal Air Force (RAF) squadrons, four Royal Canadian Air Force (RCAF), three South African Air Force (SAAF) and two Royal Australian Air Force (RAAF) squadrons serving with RAF formations, used P-40s. The first units to convert were Hawker Hurricane squadrons of the Desert Air Force (DAF), in early 1941. The first Tomahawks delivered came without armor, bulletproof windscreens or self-sealing fuel tanks, which were installed in subsequent shipments. Pilots used to British fighters sometimes found it difficult to adapt to the P-40's rear-folding landing gear, which was more prone to collapse than the lateral-folding landing gear of the Hawker Hurricane or Supermarine Spitfire. In contrast to the "three-point landing" commonly employed with British types, P-40 pilots were obliged to use a "wheels landing": a longer, low angle approach that touched down on the main wheels first.
Testing showed the aircraft did not have the performance needed for use in Northwest Europe at high-altitude, due to the service ceiling limitation. Spitfires used in the theater operated at heights around 30,000 ft (9,100 m), while the P-40's Allison engine, with its single-stage, low altitude rated supercharger, worked best at 15,000 ft (4,600 m) or lower. When the Tomahawk was used by Allied units based in the UK from February 1941, this limitation relegated the Tomahawk to low-level reconnaissance with RAF Army Cooperation Command and only No. 403 Squadron RCAF was used in the fighter role for a mere 29 sorties, before being replaced by Spitfires. Air Ministry deemed the P-40 unsuitable for the theater. UK P-40 squadrons from mid-1942 re-equipped with aircraft such as Mustangs
The Tomahawk was superseded in North Africa by the more powerful Kittyhawk ("D"-mark onwards) types from early 1942, though some Tomahawks remained in service until 1943. Kittyhawks included many improvements and were the DAF's air superiority fighter for the critical first few months of 1942, until "tropicalised" Spitfires were available. In 2012, the virtually intact remains of a Kittyhawk were found; it had run out of fuel in the Egyptian Sahara in June 1942.
DAF units received nearly 330 Packard V-1650 Merlin-powered P-40Fs, called Kittyhawk IIs, most of which went to the USAAF, and the majority of the 700 "lightweight" L models, also powered by the Packard Merlin, in which the armament was reduced to four .50 in (12.7 mm) Brownings (Kittyhawk IIA). The DAF also received some 21 of the later P-40K and the majority of the 600 P-40Ms built; these were known as Kittyhawk IIIs. The "lightweight" P-40Ns (Kittyhawk IV) arrived from early 1943 and were used mostly as fighter-bombers. From July 1942 until mid-1943, elements of the U.S. 57th Fighter Group (57th FG) were attached to DAF P-40 units. The British government also donated 23 P-40s to the Soviet Union.
Tomahawks and Kittyhawks bore the brunt of Luftwaffe and Regia Aeronautica fighter attacks during the North African campaign. The P-40s were considered superior to the Hurricane, which they replaced as the primary fighter of the Desert Air Force.
The P-40 initially proved quite effective against Axis aircraft and contributed to a slight shift of momentum in the Allies' favor. The gradual replacement of Hurricanes by the Tomahawks and Kittyhawks led to the Luftwaffe accelerating retirement of the Bf 109E and introducing the newer Bf 109F; these were to be flown by the veteran pilots of elite Luftwaffe units, such as Jagdgeschwader 27, in North Africa. The P-40 was generally considered roughly equal or slightly superior to the Bf 109 at low altitude but inferior at high altitude, particularly against the Bf 109F. Most air combat in North Africa took place well below 16,000 ft (4,900 m), negating much of the Bf 109's superiority. The P-40 usually had an advantage over the Bf 109 in horizontal maneuvers (turning), dive speed and structural strength, was roughly equal in firepower but was slightly inferior in speed and outclassed in rate of climb and operational ceiling.
The P-40 was generally superior to early Italian fighter types, such as the Fiat G.50 and the Macchi C.200. Its performance against the Macchi C.202 Folgore elicited varying opinions. Some observers consider the Macchi C.202 superior. Caldwell, who scored victories against them in his P-40, felt that the Folgore was superior to the P-40 and the Bf 109 except that its armament of only two or four machine guns was inadequate. Other observers considered the two equally matched or favored the Folgore in aerobatic performance, such as turning radius. Aviation historian Walter J. Boyne wrote that over Africa, the P-40 and the Folgore were "equivalent". Against its lack of high-altitude performance, the P-40 was considered to be a stable gun platform, and its rugged construction meant that it was able to operate from rough front line airstrips with a good rate of serviceability.
The earliest victory claims by P-40 pilots include Vichy French aircraft, during the 1941 Syria-Lebanon campaign, against Dewoitine D.520s, a type often considered to be the best French fighter of the war. The P-40 was deadly against Axis bombers in the theater, as well as against the Bf 110 twin-engine fighter. In June 1941, Caldwell, of No. 250 Squadron RAF in Egypt, flying as F/O Jack Hamlyn's wingman, recorded in his log book that he was involved in the first air combat victory for the P-40. This was a CANT Z.1007 bomber on 6 June. The claim was not officially recognized, as the crash of the CANT was not witnessed. The first official victory occurred on 8 June, when Hamlyn and Flt Sgt Tom Paxton destroyed a CANT Z.1007 from 211a Squadriglia of the Regia Aeronautica, over Alexandria. Several days later, the Tomahawk was in action over Syria with No. 3 Squadron RAAF, which claimed 19 aerial victories over Vichy French aircraft during June and July 1941, for the loss of one P-40 (and one lost to ground fire).
Some DAF units initially failed to use the P-40's strengths or used outdated defensive tactics such as the Lufbery circle. The superior climb rate of the Bf 109 enabled fast, swooping attacks, neutralizing the advantages offered by conventional defensive tactics. Various new formations were tried by Tomahawk units from 1941–42, including "fluid pairs" (similar to the German rotte); one or two "weavers" at the back of a squadron in formation and whole squadrons bobbing and weaving in loose formations. Werner Schröer, who was credited with destroying 114 Allied aircraft in only 197 combat missions, referred to the latter formation as "bunches of grapes", because he found them so easy to pick off. The leading German expert in North Africa, Hans-Joachim Marseille, claimed as many as 101 P-40s during his career.
From 26 May 1942, Kittyhawk units operated primarily as fighter-bomber units, giving rise to the nickname "Kittybomber". As a result of this change in role and because DAF P-40 squadrons were frequently used in bomber escort and close air support missions, they suffered relatively high losses; many Desert Air Force P-40 pilots were caught flying low and slow by marauding Bf 109s.
Caldwell believed that Operational Training Units did not properly prepare pilots for air combat in the P-40 and as a commander, stressed the importance of training novice pilots properly.
Competent pilots who took advantage of the P-40's strengths were effective against the best of theLuftwaffe and Regia Aeronautica. In August 1941, Caldwell was attacked by two Bf 109s, one of them piloted by German ace Werner Schröer. Although Caldwell was wounded three times and his Tomahawk was hit by more than 100 7.92 mm (0.312 in) bullets and five 20 mm cannon shells, Caldwell shot down Schröer's wingman and returned to base. Some sources also claim that in December 1941, Caldwell killed a prominent German Experte, Erbo von Kageneck (69 kills), while flying a P-40. Caldwell's victories in North Africa included 10 Bf 109s and two Macchi C.202s. Billy Drake of 112 Squadron was the leading British P-40 ace with 13 victories. James "Stocky" Edwards (RCAF), who achieved 12 kills in the P-40 in North Africa, shot down German ace Otto Schulz (51 kills) while flying a Kittyhawk with No. 260 Squadron RAF. Caldwell, Drake, Edwards and Nicky Barr were among at least a dozen pilots who achieved ace status twice over while flying the P-40. A total of 46 British Commonwealth pilots became aces in P-40s, including seven
Europe and Mediterranean theaters
On 14 August 1942, the first confirmed victory by a USAAF unit over a German aircraft in World War II was achieved by a P-40C pilot. 2nd Lt Joseph D. Shaffer, of the 33rd Fighter Squadron, intercepted a Focke-Wulf Fw 200C-3 maritime patrol aircraft that overflew his base at Reykjavík, Iceland. Shaffer damaged the Fw 200, which was finished off by a P-38F. Warhawks were used extensively in the Mediterranean Theater of Operations (MTO) by USAAF units, including the 33rd, 57th, 58th, 79th, 324th and 325th Fighter Groups. While the P-40 suffered heavy losses in the MTO, many USAAF P-40 units achieved high kill-to-loss ratios against Axis aircraft; the 324th FG scored better than a 2:1 ratio in the MTO. In all, 23 U.S. pilots became aces in the MTO on the P-40, most of them during the first half of 1943.
P-40 pilots from the 57th FG were the first USAAF fliers to see action in the MTO, while attached to Desert Air Force Kittyhawk squadrons, from July 1942. The 57th was also the main unit involved in the "Palm Sunday Massacre", on 18 April 1943. Decoded Ultra signals revealed a plan for a large formation of Junkers Ju 52 transports to cross the Mediterranean, escorted by German and Italian fighters. Between 16:30 and 18:30 hours, all wings of the group were engaged in an intensive effort against the enemy air transports. Of the four Kittyhawk wings, three had left the patrol area before a convoy of a 100+ enemy transports were sighted by 57th FG, which tallied 74 aircraft destroyed. The group was last in the area, and intercepted the Ju 52s escorted by large numbers of Bf 109s, Bf 110s and Macchi C.202s. The group claimed 58 Ju 52s, 14 Bf 109s and two Bf 110s destroyed, with several probables and damaged. Between 20 and 40 of the Axis aircraft landed on the beaches around Cap Bon to avoid being shot down; six Allied fighters were lost, five of them P-40s.
On 22 April, in Operation Flax, a similar force of P-40s attacked a formation of 14 Messerschmitt Me 323 Gigant ("Giant") six-engine transports, covered by seven Bf 109s from II./JG 27. All the transports were shot down, for a loss of three P-40s. The 57th FG was equipped with the Curtiss fighter until early 1944, during which time they were credited with at least 140 air-to-air kills. On 23 February 1943, during Operation Torch, the pilots of the 58th FG flew 75 P-40Ls off the aircraft carrier USS Ranger to the newly captured Vichy French airfield, Cazas, near Casablanca, in French Morocco. The aircraft supplied the 33rd FG and the pilots were reassigned.
The 325th FG (known as the "Checkertail Clan") flew P-40s in the MTO and was credited with at least 133 air-to-air kills from April–October 1943, of which 95 were Bf 109s and 26 were Macchi C.202s, for the loss of 17 P-40s in combat. The 325th FG historian Carol Cathcart wrote: "on 30 July, 20 P-40s of the 317th [Fighter Squadron] ... took off on a fighter sweep ... over Sardinia. As they turned to fly south over the west part of the island, they were attacked near Sassari... The attacking force consisted of 25 to 30 Bf 109s and Macchi C.202s... In the brief, intense battle that occurred ... [the 317th claimed] 21 enemy aircraft. — Cathcart
Cathcart wrote that Lt. Robert Sederberg assisted a comrade being attacked by five Bf 109s, destroyed at least one German aircraft, and may have shot down as many as five. Sederberg was shot down and became a prisoner of war.
A famous African-American unit, the 99th FS, better known as the "Tuskegee Airmen" or "Redtails", flew P-40s in stateside training and for their initial eight months in the MTO. On 9 June 1943, they became the first African-American fighter pilots to engage enemy aircraft, over Pantelleria, Italy. A single Focke-Wulf Fw 190 was reported damaged by Lieutenant Willie Ashley Jr. On 2 July the squadron claimed its first verified kill; a Fw 190 destroyed by Captain Charles Hall. The 99th continued to score with P-40s until February 1944, when they were assigned P-39s and P-51 Mustangs.
The much-lightened P-40L was most heavily used in the MTO, primarily by U.S. pilots. Many US pilots stripped down their P-40s even further to improve performance, often removing two or more of the wing guns from the P-40F/L.
Variants and development stages
XP-40: The original Curtiss XP-40, ordered July 1937, was converted from the 10th P-36A by replacing the radial engine with a new Allison V-1710-19 engine. It flew for the first time in October 1938.
This new liquid-cooled engine fighter had a radiator mounted under the rear fuselage but the prototype XP-40 was later modified and the radiator was moved forward under the engine.
- P-40: The P-40 (Curtiss Model 81A-1) was the first production variant, 199 built.
- P-40A: One P-40 was modified with a camera installation in the rear fuselage and re-designated P-40A.
P-40B / P-40C: Revised versions of the P-40 soon followed: the P-40B or Tomahawk IIA had extra .30 in (7.62 mm) U.S., or .303 in (7.7 mm) machine guns in the wings and a partially protected fuel system; the P-40C orTomahawk IIB added underbelly drop tank and bomb shackles, self-sealing fuel tanks and other minor revisions, but the extra weight did have a negative impact on aircraft performance. (All versions of the P-40 had a relatively low power-to-weight ratio compared to contemporary fighters.)
P-40D: Only a small number of P-40D or Kittyhawk Mk Is were made, fewer than 50. With a new, larger Allison engine, slightly narrower fuselage, redesigned canopy, and improved cockpit, the P-40D eliminated the nose-mounted .50 in (12.7 mm) guns and instead had a pair of .50 in (12.7 mm) guns in each wing. The distinctive chin airscoop grew larger so they could adequately cool the large Allison engine.
Retrospective designation for a single prototype. The P-40A was a single camera-carrying aircraft.
P-40E: The P-40E or P-40E-1 was similar in most respects to the P-40D, except for a slightly more powerful engine and an extra .50 in (12.7 mm) gun in each wing, bringing the total to six. Some aircraft also had small underwing bomb shackles. Supplied to the Commonwealth air forces as the Kittyhawk Mk IA. The P-40E was the variant that bore the brunt of air-to-air combat by the type in the key period of early to mid 1942, for example with the first US squadrons to replace the AVG in China (the AVG was already transitioning to this type from the P-40B/C), the type used by the Australians at Milne Bay, by the New Zealand squadrons during most of their air-to-air combat, and by the RAF/Commonwealth in North Africa as the Kittyhawk IA.
P-40F and P-40L, which both featured Packard V-1650 Merlin engine in place of the normal Allison, and thus did not have the carburetor scoop on top of the nose. Performance for these models at higher altitudes was better than their Allison-engined cousins. The L in some cases also featured a fillet in front of the vertical stabilizer, or a stretched fuselage to compensate for the higher torque. The P-40L was sometimes nicknamed "Gypsy Rose Lee", after a famous stripper of the era, due to its stripped-down condition. Supplied to the Commonwealth air forces under the designation Kittyhawk Mk II, a total of 330 Mk IIs were supplied to the RAF under Lend-Lease. The first 230 aircraft are sometimes known as the Kittyhawk Mk IIA. The P-40F/L was extensively used by U.S. fighter groups operating in the Mediterranean Theater.
P-40G : 43 P-40 aircraft fitted with the wings of the Tomahawk Mk IIA. A total of 16 aircraft were supplied to the Soviet Union, and the rest to the US Army Air Forces. It was later redesignated RP-40G.
P-40K, an Allison-engined P-40L, with the nose-top scoop retained and the Allison-configured nose radiators scoop, cowl flaps and vertical-stabilizer-to-fuselage fillet. Supplied to the Commonwealth air forces as the Kittyhawk Mk III, it was widely used by US units in the CBI.
P-40M, version generally similar to the P-40K, with a stretched fuselage like the P-40L and powered by an Allison V-1710-81 engine giving better performance at altitude (compared to previous Allison versions). It had some detail improvements and it was characterized by two small air scoops just before the exhaust pipes. Most of them were supplied to Allied countries (mainly UK and USSR), while some others remained in the US for advanced training. It was also supplied to the Commonwealth air forces as the Kittyhawk Mk. III.
P-40N (manufactured 1943–44), the final production model. The P-40N featured a stretched rear fuselage to counter the torque of the more powerful, late-war Allison engine, and the rear deck of the cockpit behind the pilot was cut down at a moderate slant to improve rearward visibility. A great deal of work was also done to try and eliminate excess weight to improve the Warhawk's climb rate. Early N production blocks dropped a .50 in (12.7 mm) gun from each wing, bringing the total back to four; later production blocks reintroduced it after complaints from units in the field. Supplied to Commonwealth air forces as the Kittyhawk Mk IV. A total of 553 P-40Ns were acquired by the Royal Australian Air Force, making it the variant most commonly used by the RAAF. Subvariants of the P-40N ranged widely in specialization from stripped down four-gun "hot rods" that could reach the highest top speeds of any production variant of the P-40 (up to 380 mph), to overweight types with all the extras intended for fighter-bombing or even training missions. The 15,000th P-40 was an N model decorated with the markings of 28 nations that had employed any of Curtiss-Wright's various aircraft products, not just P-40s. "These spectacular markings gave rise to the erroneous belief that the P-40 series had been used by all 28 countries." Since the P-40N was by 1944 used mainly as a ground attack aircraft in Europe, it was nicknamed B-40 by pilots. Survivors redesignated as ZF-40N in June 1948.
P-40P: The designation of 1,500 aircraft ordered with V-1650-1 engines, but actually built as the P-40N with V-1710-81 engines.
XP-40Q: Three P-40N modified with a 4-bladed prop, cut-down rear fuselage and bubble canopy, four guns, squared-off wingtips and tail surfaces, and improved engine with two-speed supercharger. Even with these changes, its performance was not enough of an improvement to merit production when compared to the contemporary late model P-47Ds and P-51Ds pouring off production lines. The XP-40Q was, however, the fastest of the P-40 series with a top speed of 422 mph (679 km/h) as a result of the introduction of a high-altitude supercharger gear. (No P-40 model with a single-speed supercharger could even approach 400 mph (640 km/h)
P-40R: The designation of P-40F and P-40L aircraft, converted into training aircraft in 1944.
RP-40: Some American P-40s were converted into reconnaissance aircraft.
TP-40: Some P-40s were converted into two-seat trainers.
Twin P-40 : A single photo exists of a P-40 mocked up with two Merlin engines, mounted atop the wings, over the main landing gear