Curtiss P-40 Warhawk

The Curtiss P-40 Warhawk was an American fighter aircraft that first flew in 1938. It was a modified version of the Curtiss P-36 Hawk. The P-40 would become a successful aircraft that served in with many Allied air forces until after the Second World War. When production ceased in November 1944, a total of 13,738 of various types had been manufactured. The aircraft was known as Warhawk to the Americans. Among the other Allies, the early types were known as Tomahawk and the later ones as Kittyhawk. The aircraft was particularly successful as a fighter aircraft for lower altitudes and as an escort fighter and fighter-bomber. The aircraft took part in almost all theatres of war during the Second World War.

Curtiss Kittyhawk Mark III, No. 112 Squadron, RAF, Medenine, May 1943. Source: Imperial War Museum TR 975

When Curtiss was developing its model 75 (Curtiss P-36), it was already acknowledged that the use of a radial engine in combination with prevailing technical developments would lead to shortcomings. The cause was mainly due to the type of engine used, which at that time was incapable to generate more than 1,200 hp in power output. Two options were presented to solve the problem. Firstly, one could look for aerodynamic solutions, something that was certainly not easy with a radial engine (a problem that Germany only managed to solve with great difficulty with the Focke Wulf Fw 190), or secondly, opt for the use of an in-line engine. In 1936 it was decided to try their luck with the latter. For this purpose, Curtiss selected the Allison V-1710 series.

Curtiss XP-37. Source: Curtiss photo

The P-36 design was chosen as the basis and adapted for the newly selected engine. Powered by a 1,150 hp Allison V-1710-11 engine, an aircraft was created of which the first made its maiden flight in April 1937 as XP-37. Despite many engine problems, the XP-37 managed to set a new speed record of 483 km/h. The USAAC (United States Army Air Corps, as the American Air Force was then called) ordered 13 YP-37 test aircraft, of which the first was ready in June 1939. A newer version of the engine was chosen for the YP-37, an Allison V-1710-21. As a result, the overall length of the YP-37 was extended behind the cockpit by 0.635 meter. Also, some aerodynamic improvements were catered for. However, the aircraft appeared to experience unsolvable problems in the propulsion system and all YP-37 aircraft were eventually withdrawn from the USAAC in 1942.

Curtiss YP-37. Source: US Army photo

The problems were solved by building a new test aircraft based on the 10th P-36A airframe with a 1,150 hp Allison V-1710-19 engine, the Model 75P. The USAAC registered it as XP-40. The frame was extensively modified and for the first time the XP-40 started to resemble some of the characteristic appearance of the later P-40s. The aircraft was initially armed with a 12.7 mm and a 7.62 mm machine gun, but this was soon replaced by two 12.7 mm machine guns built into the top of the nose. Racks were fitted under the wings to carry a total of six 9.1 kg bombs, making the aircraft a potential fighter-bomber.

On October 14, 1938, the XP-40 took to the air and achieved a disappointing maximum speed of 481 km/h. The radiator, much too small and originally mounted on the top of the nose, was removed and integrated with the oil cooler underneath the nose. Now the shape of the P-40 really started to show itself, and its speed increased to 550 km/h.

Curtiss YP-37. Source: US Army photo

The XP-40 was subjected to a test program by the USAAC together with the Lockheed XP-38, Bell XP-39 as well as the Republic XP-41 and XP-43. Whereas its performance did not match that of the other aircraft, cheaper and faster production was ultimately the decisive factor, even though the other aircraft were ordered as well. Some other modifications were made in March and April 1939 and by means of an Allison V-1710-33 (C15) engine the speed was increased to 587 km/h. The aircraft was put into production, whereby the USAAC assigned it a future role as a fighter for low- and medium-altitude combat and for coastal defence.

Mainly because of the low production costs and the capacity to manufacture fast and in large quantities, the USAAC decided in April 1936 to purchase 534 P-40s. This production version would be the same as the XP-40, except for the engine. The 1,040 hp Allison V-1710-33 (C15) engine now became the standard. The armament consisted of the prevailing standard USAAC armament: two 12.7 mm Browning M2 machine guns mounted in the top of the nose. To increase fire power in the future, accommodations were made to install a 7.62 mm machine gun in each wing. To limit weight and because the USAAC did not consider these extras necessary at the time, no armour plating, armoured windshield and self-sealing fuel tanks were initially fitted. A novelty for that time was the fully retractable tail wheel.

The first example flew on April 4th, 1940, and deliveries started from May that same year. The first three aircraft were used for extensive test flights. The P-40s were assigned serial numbers 39-156 to 39-280, 40-292 to 40-357. The aircraft entered service with the 8th Pursuit Group at Langley Field, Virginia, followed by the 20th Pursuit Group, North Field, California, 31st Pursuit Group, Selfridge Field, Michigan and 35th Pursuit Group.

Curtiss-Wright P-40, 8th Pursuit Group, Langley Field, Virginia, 1940. Source: Public Domain (unknown)

Two examples of this type were preserved and are on display at the Air Power Park and Museum, Hampton, Virginia and the March Field Air Museum, Riverside, California.

The fact that no more than 199 P-40 aircraft were manufactured had everything to do with the latitude that the Curtiss factory was granted by the American government to produce an export version of the P-40. The first buyer was the French Armée de l'Air that ordered 140 aircraft of this export version, the model H81-A. Although the first aircraft, already in French colours, were ready for delivery by the factory as early as April 1940, this was foiled by the German invasion of France. The French aircraft would be armed with four 7.5 mm Browning FN model 1938 machine guns in the wings and outfitted with French equipment.

At the same time, the British RAF suffered a major shortage of fighter aircraft and requested to take over the French order. In September 1940, permission was granted, so that the first P-40s, called Tomahawk Mk I in Great Britain, could reach England the same month. The British aircraft retained the 12.7 mm machine guns in the nose but were supplemented with four 7.62 mm British (Cal .303) Brownings integrated in the wings (two per wing). In some cases, the 12.7 mm machine guns in the nose were later replaced by more readily available 7.62 mm machine guns.

Tomahawk Mk I AH769, Boscombe Down. Source: Public Domain (unknown)

Of the 140 aircraft (RAF serial numbers AH741 to AH880), three (serial numbers AH774, AH793 and AH840) went to Canada for training purposes and the rest arrived in Great Britain. The need was so urgent that some aircraft arrived at their operational bases with French equipment on it. Although the aircraft was unsuitable for combat due to a lack of armour and self-sealing fuel tanks, the need of fighters was so urgent that the aircraft were immediately put into combat operations with RAF Squadrons No. 2, 26, 171, 231, 239, 250, 268 and 613 and British-based RCAF squadrons No. 400 and 403. After the threat of a German invasion had subsided, the Tomahawk Mk I's were soon removed from the squadrons, and some were given a new role as trainers. However, the aircraft would still be deployed in North Africa, where at that time they mainly had to deal with Italian aircraft that had fewer armament. The Desert Air Force Squadron No. 112 would become the first to replace its Gloster Gladiators with the Tomahawk Mk I.

The designation P-40A was never assigned to a factory series. Only one aircraft, P-40 serial no. 40-326, was designated as such after having been converted into a photo reconnaissance plane in 1942.

Due to the export production of Curtiss, the USAAC needed replacements, and a new order for P-40s was put in during September 1940. The first combat experiences in Europe had shown that the standard P-40 was too lightly armed and that the lack of armour made the aircraft unsuitable for warfare. This resulted in the P-40B (Model 81B) with increased ammunition storage for the two 12.7 mm machine guns in the nose and the installation of two additional 7.62 mm machine guns in the wings, armoured windshield, pilot armour, and self-sealing fuel tanks. No changes were made to the engine, so performance decreased due to the extra weight.

131 Aircraft (serial numbers 41-5205 to 41-5304 and 41-13297 to 41-13327) were ordered, production of which started in January 1941. The first aircraft flew on March 13th, 1941. In 1943 the remaining aircraft were withdrawn and went to training units as RP-40B.

P-40B, American Volunteer Group, China. Source: Public Domain (unknown)

One aircraft of the P-40B has been preserved and is on display in the National Museum of Naval Aviation at NAS Pensacola, Florida.

The export version of the P-40B became Model H81-A2. The RAF purchased 110 aircraft (AH881 to AH990) directly from the Curtiss factory as Tomahawk IIA. The armament was similar to that of the original P-40B, but with British-made Brownings in the wings. The aircraft were equipped with British radio equipment and externally sealed fuel tanks. The Soviet Union Air Force received 23 (AH936, AH952, AH965 to AH971, AH974 to AH985, AH987, AH989 and AH990) of these aircraft from the RAF and Canada received one (AH938) for training purposes.

Tomahawk Mk. IIA, AH965, 126 IAP PVO, Moscow, December 1941. Source: Public Domain (unknown)

The Mk IIAs mainly ended up in Great Britain with RAF squadrons 2, 26, 231, 239, 241, 400 and 414 and were used intensively for fighter attacks above enemy territory from 1941 to early 1942.

The next series to supplement the original order consisted of 193 aircraft (serial numbers 41-13328 to 41-13520) of the Model H81-B. However, the USAAC gave this the designation P-40C because of the different fuel system, with improved self-sealing fuel tanks and the possibility of carrying an external, jettisonable extra fuel tank under the fuselage. In addition, the aircraft were equipped with a different radio system (SCR-247N instead of the usual SCR-283). Because the original engine was retained, the additional weight caused further limitations in performance.

P-40C, 8th Pursuit Group, 33rd Pursuit Squadron, Mitchel Field, 1941. Source: Public Domain (unknown)

In 1944 the last P-40C aircraft was transferred to second-line duties as RP-40C.

The export version of the P-40C was Model H81-A2 and named Tomahawk Mk IIB by the British. The armament was the same as the P-40C. The P-40C differed from the Tomahawk Mk IIA version in the use of American equipment (such as the radio) instead of British, the fuel tanks that self-sealed from the inside and the provision for a drop tank under the fuselage.

No fewer than 930 Tomahawk Mk IIB were built in four batches. The first batch included serial numbers AH991 to AH999 that were delivered to the Soviet Union. Of the next batch (serial numbers AK100 to AK570), at least 36 aircraft went to China for the AVG (American Volunteer Group) and the AK210 to AK224 and AK226 to AK241 were lost during overseas transport. From the third batch (serial numbers AM370 to AM 519), another 64 aircraft went to the AVG. The last batch included AN218 to AN517. A total of 23 Tomahawk IIBs went to the Soviet Union (the AH series and some from the AN series). In November, an unknown number of aircraft were transferred to the Turkish Air Force and later the AK254, AK434, AK440, AK448, AK470 and AK561 went to the Egyptian Air Force. Most IIBs ended up in North Africa, where they were deployed with RAF squadrons No. 73, 112, 250 and 260, the RAAF squadron No. 2 and the SAAF squadrons No. 2,4,5 and 40.

Curtiss Tomahawk Mk IIB, AVG China. Source: Public Domain (unknown)

One ex-Soviet aircraft has been preserved and restored in the colours of the AVG.

Both the P-40B and P-40C were delivered to various overseas fighter units in the USAAC. It was these two types of fighter aircraft that had to engage in combat when Japan started the war in the Far East at full speed. At the time of the Japanese attack on Pearl Harbor on December 7th, 1941, at least 99 P-40s were stationed in Hawaii, as well as 87 P-40Bs and 12 P-40Cs. The 15th and 18th Pursuit Groups were stationed at Wheeler. During the first wave of attacks, at least 62 P-40Bs were destroyed on the ground. Four P-40Bs succeeded in attacking the enemy and shot down at least five Japanese aircraft. Of the 12 P-40Cs, 7 were destroyed on the ground and 3 were shot down. After the Japanese attacks, 25 P-40Bs and 2Cs remained in Hawaii. At Clark Field in the Philippines, the 20th Pursuit Squadron of the 24th PG was equipped with P-40s, whose fate was no less unfortunate as what had happened in Hawaii.

P-40B aircraft destroyed during the Japanese attack on Pearl Harbor. Source: US Army photo

Initially, the British Tomahawks were more successful in the North African desert. In the early phase, the enemy here consisted of the much inferior Italian fighter aircraft. The Tomahawk’s ability to sustain a lot of damage made the aircraft perfect for supporting assaulting ground troops and attacking retreating enemy forces. Because many actions in the deserts took place at low altitude, the Tomahawk could even compete against the German Messerschmitt Bf 109.

The P-40 probably became most famous due to the actions of the American Volunteer Group (AVG) in China. This unit of American volunteers fought on the Chinese side, under British command, against the Japanese invasion of China. There is much disagreement about exactly what type of aircraft was initially supplied to the AVG. According to the factory records these must have been Tomahawk IIBs (P-40C). However, witnesses have repeatedly stated that the AVG aircraft could not carry external fuel tanks, which equated them to the Tomahawk IIA. The aircraft also displayed other changes (type of fuel tanks and lack of armour) that indicate these were more likely to have been the IIA, rather than the IIB. However, the aircraft did indeed originate from a purchase order for Tomahawk IIBs. Probably because the aircraft were ordered by the Chinese government, without extras, they were completed with parts intended for Tomahawk Mk IIAs, which the British government no longer considered suitable. As such, the Curtiss factory easily got rid of excess spare parts. Although the unit consisted of volunteers for the Chinese army, the AVG only really came into action after Japan attacked Pearl Harbor and provoked the United States to enter the war. The Tomahawks served with the AVG until March 1942, after which they were replaced by P-40E aircraft.

Before moving on to the next model, we’ll first discuss the P-40G as it was directly derived from the first P-40 series. In 1940, a P-40 (serial number 39-221) during its construction was experimentally fitted with wings intended for the H81-A2 Tomahawk IIA to evaluate whether it could be upgraded with an additional armament of four 7.62 mm machine guns in the wings. This aircraft was unofficially designated XP-40G.

Between August and September 1941, 43 USAAC P-40s were also converted to the Model 81-AG. The aircraft subsequently returned to operational service as P-40G. It is not entirely certain which serial numbers the aircraft were assigned, but the most authoritative sources classify these as 42-14261 to 42-14274, 42-14277 to 42-14278 and 42-14281.

In October 1941, 16 of these planes were sent to the Soviet Union. The remainder entered second-line duties as RP-40G in October 1942.

When production of the earlier P-40 models was in full swing in early 1940, further development of the type was taken up by Curtiss. Various adjustments had taken their toll in the meantime. By adding armour plating, additional armament and self-sealing fuel tanks, the weight had increased considerably which reduced the aircraft’s performance. Curtiss and the engine manufacturer Allison discussed the issue, which led to the design of an improved version of the V-1710 engine, the V-1710-39 (F3R). This engine delivered significantly more power, without losing it at higher altitudes.

P-40D during a test flight above Buffalo. Source: Public Domain (unknown)

The shorter shape of this engine allowed the nose section of the P-40 to be completely redesigned. The nose became shorter and narrower in size. At the same time, the pilot's rear view was improved, the landing gear could be shortened slightly, and the shape of the nose became more streamlined. As the nose had been narrowed, it could no longer accommodate weapons which were then positioned in the wings. The standard armament was four 12.7 mm machine guns. The re-configurated aircraft was given the factory designation Model H87. However, the military designation stuck to the P-40 series and aircraft was named the P-40D, which would soon receive the American nickname Warhawk. The weapons were installed in such a way that two 12.7 mm machine guns could be replaced by two 20 mm guns. However, this option was never used. The aircraft could carry either a jettisonable fuel tank or a 227 kg bomb under the fuselage. Six 9.1 kg bombs or four 23 kg bombs could also be carried under the wings.

This time it was the British that placed the first order, under the new name Kittyhawk Mk I. The USAAC only ordered its first P-40Ds in June 1940, two weeks after delivery of the first British aircraft. Deliveries started in July 1941. Only 23 aircraft were delivered, because the USAAF decided to switch to a different standard armament. The aircraft were given the serial numbers 40-359 to 40-381. In 1943 the remaining aircraft entered second-line duties as RP-40D.

The first export model of the P-40D was the Model H87A-1, initially ordered by France. However, this order was cancelled due to the German invasion of France. Before even one P-40D had been produced, the British RAF ordered a total of 560 aircraft of the export model H87A-2. The RAF serial numbers were AK571 to AK999 and AL100 to AL230 and delivery started in August 1941. RAF Squadron 112 in North Africa was equipped with these aircraft on December 1, 1941, and decorated with a shark's mouth they caused quite a sensation. Squadrons No 94, 250 and 260 followed a short time later. In addition, Squadrons No 5 and 7 SAAF and No 3 RAAF, operating in North Africa, also had availed of the aircraft.

Kittyhawk Mk I, AK596, No. 94 Squadron, North Africa. Source: Imperial War Museum CM 2008

Canada received 72 aircraft directly from the RAF series. In Canada they were assigned serial numbers 1028 to 1099. Later, another 17 aircraft were delivered to the Turkish Air Force. The Canadian aircraft all operated in Canada with No 14, 111, 118, 130, 132 and 133 Squadron. In May 1942, No.111 Squadron left for Alaska to assist the Americans in their fight against the Japanese around the Aleutian Islands.

At least one Canadian aircraft has been preserved and can be viewed at the Canada Aviation Museum in Ontario.

After 23 P-40Ds had been produced for the USAAC, production was converted to a new type. Meanwhile, it had been decided to increase the standard armament to six 12.7 mm machine guns in the wings (three per wing). The aircraft was given the factory designation Model H87B-2 and became the P-40E with the USAAC. The P-40E was also able to carry a 45 kg bomb under each wing.

Delivery took place from August 1941. The USAAF - the Corps had meanwhile been transformed into an independent Air Force - serial numbers were 40-358, 40-382 to 40-681, 41-5305 to 41-5744 and 41-13521 to 41-13599. Two aircraft were equipped with dual controls and used as TP-40E trainers.

In the Philippines, the 3rd Pursuit Squadron had just switched to the P-40E whereas the other squadron (No. 17) of No 24 Pursuit Group was still in process at the time of the Japanese attack. There was a total of 74Es present, most of which were destroyed on the ground by surprise.

P-40E, 11th Pursuit Squadron. Source: Wilco Vermeer collection

After the fall of the Philippines, the 24th Group was re-equipped with P-40Es in Australia and from there the aircraft were deployed to Java in January 1942 to continue the fight against Japan. Of the 74 aircraft sent, only 38 ultimately managed to reach Java due to various reasons. Thirty other aircraft intended for Java eventually reached the American Volunteer Group (AVG) in China, via Ghana, to replace the outdated Tomahawks. The AVG would be disbanded in July 1942 and merged as the 23rd Pursuit Group, with the74th, 75th and 76th Pursuit Squadrons No 74, 75 and 76. From that moment on, the AVG was again part of the American air force.

Other P-40Es ended up with the 11th and 18th Pursuit Squadrons of the 28th Composite Group in Alaska and from there were deployed in operations over the Aleutian Islands.

P-40Es are currently on display at the Hill Aerospace Museum, Hill Airforce Base, Utah, at the National Air and Space Museum, Washington, at the San Diego Aerospace Museum, San Diego, California, at the United States Air Force Museum, Wright-Patterson, Ohio and at the War Eagles Air Museum, Santa Teresa, New Mexico.

The export version of the P-40E became the Kittyhawk Mk IA. It was the first P-40, which was entirely delivered according to the Lend-Lease concept. No less than 1500 aircraft of the Kittyhawk Mk IA were produced. Originally they were all going to be delivered to the RAF, but through the Lend-Lease system they ended up in many other air forces.

The Kittyhawk Mk IA was not entirely identical to the P-40E, but partly equipped with British equipment. As a result, this version received its own factory designation, Model H87A-4, while it was registered with the USAAF as P-40E-1. The Lend-Lease terms required that the aircraft be transferred with American serial numbers. Nevertheless, they were also initially given RAF numbering. The series were 41-24776 to 41-25194 (RAF ET100 to ET519) and 41-35874 to 41-36953 (RAF ET520 to ET999 and EV100 to EV699). Several of these aircraft were transferred to other countries. Australia received 163 aircraft (A29-1 to A29-163) for the RAAF and the Canadian RCAF received twelve aircraft (720 to 731). The RNZAF received no fewer than 134 Kittyhawk Mk IAs (serial numbers NZ3001 to NZ 3044, NZ3091 to NZ3098, NZ3100 to NZ3180 and NZ3271). Six aircraft went to the Forca Aerea Brasileira (Brazil) in 1942.

Curtiss Kittyhawk Mk IA, 41-36504, still featuring American registration. Source: Public Domain (unknown)

The following Kittyhawk Mk IA aircraft have been preserve: NZ3009 can be viewed in Duxford, England, NZ3039 is present at MoTaT, New Zealand, and NZ3043 is stored with Mr J. Smith in Mapua. The restoration of NZ3094 is underway in Australia. A former Soviet-owned aircraft is also currently being restored in New Zealand.

What is less known is that the Japanese air force also had an operational unit equipped with P-40E aircraft. This unit was stationed in Rangoon, at the Mingalodon air base and was responsible for defending the airspace there. It is not known where the aircraft originally came from, but they were most likely left behind in the Philippines or Java.

Unit with Japanese P-40 aircraft. Source: Wilco Vermeer collection

To this day it is unknown why the Japanese army command decided to equip an entire unit with confiscated P-40Es. The aircraft must have been transferred via Malacca to Burma in March 1943, because it is known that several flights were spotted making stops at Alor Star air base around that time. The aircraft belonged to the 50th Hikosentai, as they bore characteristics of that unit. There are photos of Japanese P-40s, but they do not indicate to which operational unit they were assigned.

Slowly but surely, the need arose to be able to deliver better performance with the P-40 at higher altitudes. As a test, a P-40D (serial number 40-360) was equipped with a 1300 hp Rolls Royce Merlin 28 engine. This is how the Model 87B-3 prototype, the XP-40F, was born. The engine proved to have much better performance than the Allison engines and was manufactured under license by Packard as the V-1650-1.

A total of 1,311 aircraft were ordered under the type designation P-40F. Henceforth, the name Warhawk was officially adopted for the P-40. After the first 699 aircraft were delivered, a new numbering system was introduced with the USAAF, so that minor changes could still remain within the same type designation. The first 699 P-40Fs (serial numbers 41-13600 to 41-14299, of which number 41-13696 was cancelled), would have been referred to as P-40F-1-CU if that new number system had been introduced earlier, whereby the CU stood for "built by Curtiss".

Curtiss P-40F, 44th Fighter Squadron, Guadalcanal. Source: Wilco Vermeer collection

With a slightly longer fuselage, 123 aircraft (serial numbers 41-14300 to 41-14422) were produced as P-40F-5-CU. The hull was extended to achieve better stability with the heavier engine. Henceforth, this longer fuselage became standard for all subsequent P-40 series. A further change in the operation of the cooling valves (manual instead of electric) resulted in the P-40F-10-CU, of which 177 were built (serial numbers 41-14423 to 41-14599). A winter version was released as P-40F-15-CU, especially for operations in colder areas, of which 200 aircraft would be built (serial numbers 41-19733 to 41-19932). Finally, a type with an improved oxygen system for the pilot followed as P-40F-20-CU, of which 112 aircraft were delivered (serial numbers 41-19933 to 41-20044).

A total of 37 P-40F aircraft were transferred to the Free French.

Of the 1,311 P-40F aircraft manufactured, 230 were delivered to the RAF from January 1942 under the Lend-Lease system. These aircraft were given the designation Kittyhawk Mk IIA, with the RAF serial numbers FL219 to FL448. The problem with this, however, is that the same delivery also included P-40F aircraft converted into P-40L (Kittyhawk Mk II). Therefore, it is hard to tell from the RAF serial numbering whether it is an F- or an L-type. Most of these aircraft were not delivered to the RAF itself. FL273 and FL369 to FL448 were delivered to the USAAF in 1942 and 1943 for use in the invasion of North Africa. Eleven aircraft (FL230 to FL232, FL235, FL236 and FL239 to FL240) were lost during transport by sea to England. Seven aircraft (FL263, FL270, FL276, FL280, FL283, FL305 and FL307) were transferred to the Free French Air Force (Groupe de Chasse II/5), also for use in North Africa. One hundred aircraft went to the Soviet Union.

For experiments with the cooling system and tail rudder, one aircraft (serial number 41-13602) was returned to the factory and converted into YP-40F. The cooler was moved to the rear and other smaller changes were made.

Kittyhawk IIA, FL220. Source: Imperial War Museum ATP 10932C

The P-40G has been discussed before and the P-40H type was never built. Because the I was too similar to the number I, this designation was never used. The next P-40 version became the P-40J. This would be a P-40E with a tuned-up engine. However, the project was canceled in May 1942.

Because the Merlin engines could not be produced quickly enough in sufficient quantities the trusted Allison engines were once again utilised, albeit a stronger type: the 1325 hp Allison V-1710-73 (F4R). In October 1941, 600 aircraft were initially ordered for a Lend-Lease program for China. This became the P-40K-1-CU which was in fact a P-40E in the short version. Most aircraft were sent abroad via a Lend-Lease construction. Initially, the aircraft were assigned serial numbers 42-45722 to 42-46321.

Curtiss P 40K-1-CU Warhawk, 42-46319, Aleutians, Alaska. Source: US Army photo

Nine P-40K-1 aircraft were sold to Canada, where they continued to fly with American registration numbers. Most ultimately continued to fly with the USAAF in China and Burma, with the 3rd and 5th Fighter Groups of the 1st Chinese American Composite Wing. The Soviet Union would receive a total of 170 P-40Ks.

The next 200 aircraft received a better cooling system and were designated P-40K-5-CU. These were similar in design to the P-40E. To achieve better stability with the stronger engine, a kind of dorsal fin as an extension forward of the tail section was initially chosen instead of the extended fuselage of later versions. The aircraft were given serial numbers 42-9730 to 42-9929.

From the P-40K-10-CU version onwards, the longer fuselage was introduced which became standard for the following P-40s. Of these, 335 aircraft were produced with serial numbers 42-9930 to 42-10264. A winter version was released as P-40K-15-CU especially for use in colder areas such as Alaska. A total of 165 aircraft were built with serial numbers 42-10265 to 42-10429.

A total of 192 P-40K-1-CU aircraft went to the RAF under the name Kittyhawk Mk III. The first aircraft arrived in the Middle East at the end of 1942. The RAF serial numbers were FL875 to FL905, FR111 to FR115, FR210 to FR361 and FL710 to FL713. The same designation was used for 42 aircraft of the type P-40K-10-CU (serial numbers A29-164 to A29-203) and type P-40K-15CU (serial numbers A29-204 to A29-205) for the RAAF, 23 P-40K-1-CU aircraft for the RNZAF (serial numbers NZ3045 to NZ3065, NZ3090 and NZ3099.

Kittyhawk III, FR303, OK-Z, No. 450 Squadron RAAF, Libya, 1943. Source: Public Domain (unknown)

Brazil received a total of 31 P-40K-1-CU, P-40K-10-CU and P-40K-15-CU aircraft from November 1942.

To test some proposed improvements, P-40K-10-CU aircraft 42-10219 was equipped with an Allison V-1710-43 engine and designated XP-40K. This particular aircraft regularly changed its appearance following various experiments.

An unknown number of aircraft were equipped with dual controls and used as TP-40K trainers.

The many changes to the P-40 models caused a significant increase in weight, followed by a corresponding decrease in performance. The developments in the engines could not sufficiently compensate for this. In an effort to improve performance, an effort was made to reduce weight.

This gave rise to the P-40L. This was in fact a P-40F-5-CU, stripped of a number of weight-adding features. Armament was reduced from six to four machine guns, fuel capacity was reduced and some armour was removed. Furthermore, the type was identical to the P-40F-5-CU. It was not a great success and the aircraft had only become slightly faster.

P-40L, 461st Bomb Group. Source: Wilco Vermeer collection

Five variants were produced. The first, P-40L-1-CU, had its weight reduced without affecting fuel quantity and armament. Of these, 50 aircraft were produced with serial numbers 42-10430 to 42-10479.

Two machine guns were removed as well as the forward fuel tanks in the wings of the P-40L-5-CU. A total of 220 aircraft were produced with serial numbers 42-10480 to 42-10699.

The 148 P-40L-10-CU aircraft produced were similar to the P-40L-5-CU with modifications in electrical equipment and engine controls. These aircraft were given serial numbers 42-10700 to 42-10847.

With adjustments to the air filters and signalling lighting, 112 P-40L-15-CU aircraft were built in the series 42-10848 to 42-10959.

The last version of the P-40L constituted of 170 P-40L-20-CU aircraft with serial numbers 42-10960 to 42-11129 whereby modifications had been made to the electrical system and radio equipment.

Based on a Lend-Lease construction, the RAF received 100 P-40L-1-CU aircraft under the name Kittyhawk Mk II. These aircraft were given serial numbers FS400 to FS499. Oddly enough, a second series of 160 identical aircraft (serial numbers FL714 to FL730, FR116 to FR140, FR385 to FR392 and FR413 to FR521) were named Kittyhawk Mk III. This designation was also given to P-40K and P-40M aircraft, which understandably caused some confusion about which type certain series actually belonged to.

Squadron No 3 (RAAF), assigned to the RAF, was also equipped with this type; so, formally it was also delivered to Australia (albeit with RAF serial numbers).

The Free French were also allocated 36 RAF aircraft for their air force. One aircraft (Kittyhawk Mk II, Nr. NZ3074) was delivered to New Zealand.

Due to the shortage of the Merlin engines built under license by Packard, a version with an Allison engine was introduced with the introduction of the P-40L, the 1200 hp powered V-1710-81. The resulting aircraft became the P-40M. Due to the same production line as the P-40L, the P-40M became operational slightly earlier in November 1942. The aircraft was almost identical to the P-40K-20-CU, except for the engine.

Based on minor differences of certain components, three versions are distinguished. The first 60 P-40M-1-CU aircraft had serial numbers 43-5403 to 43-5462. Of the next series, 260 aircraft were built as P-40M-5-CU with serial numbers 43-5463 to 43-5722. The biggest change was the last series of 280 aircraft, which involved an overhaul of the landing gear. This series is known as P-40M-10-CU (serial numbers 43-5723 to 42-6002). Most P-40Ms were designed as Lend-Lease Kittyhawk Mk III. The Americans have used various versions in China and the Mediterranean.

The RAF received a total of 264 aircraft with serial numbers FR779 to FR872 and FS100 to FS269. The RAF equipped the South African Nr. 5 SAAF Squadron, amongst others, with this aircraft.

No fewer than 168 aircraft went to Australia. The different versions are known fairly accurately. Serial numbers A29-300 to A29-309, A29-330 to A29-331 and A29-337 to A29-344 belonged to type P-40M-1-CU. The A29-310 to A29-329, A29-332 to A29-336 and A29-355 to A29-364 belonged to the P-40M-5-CU type. The other series (A29-345 to A29-354 and A29-365 to A29-389) belonged to the P-40M-10-CU type.

With serial numbers NZ3066 to NZ3073, NZ3075 to NZ3089, NZ3109 to NZ3119 and NZ3180, 34 aircraft went to New Zealand. A total of 19 P-40Ms went to the Brazilian Air Force. According to sources that have not yet been confirmed, a total of around 170 Kittyhawk Mk III aircraft were shipped to the Soviet Union. A Russian P-40M had to make an emergency landing in Finland in December 1943 and was immediately incorporated into the Finnish Air Force as the KH-51.

The 43-5802 has been preserved and continues to fly as part of "The Fighter Collection" in Duxford, England. In New Zealand, NZ3119 has been preserved and is being restored.

The last version that was to be produced in large quantities was also the most produced version of the P-40, the P-40N. In an attempt to continue to compete against newer types of the P-38, P-47 and P-51, Curtiss diligently sought to thoroughly modernise the design of the P-40 without having to make major adjustments to the production process. In this way the factory models Model 87V and 87W were created.

Due to the lack of licensed Packard-Merlin engines, it was decided to present a version based on the 1200 hp Allison V-1710-81 engine and this became the P-40N. The entire structure was modified with lighter metals, a reduction in the number of machine guns (from six to four), smaller and lighter landing gear and improved armour. This created the fastest P-40 type ever to be built. Despite the fact that the type was already outdated according to the standard applicable in 1943, it would still become the most produced and used P-40, in no fewer than seven versions.

The first version, the P-40N-1-CU, appeared in March 1943 and was powered by the Allison V-1710-81 engine. The N-1 became the fastest P-40 version ever manufactured till then and was specially intended for high-altitude operations. A total of 400 aircraft would be built, initially with serial numbers 42-104429 to 42-104828.

Major improvements to the pilot's view resulted in modifications to the cockpit canopy. The armament was increased again to six machine guns. Suspension points for bombs or fuel tanks were attached to the wings, in addition to the existing option to carry a bomb or fuel tank under the fuselage. All this increased the weight, which reduced the top speed. No fewer than 1,100 aircraft of this version, the P-40N-5-CU, were produced. Once they arrived at operational units, a total of 30 aircraft were converted into photo reconnaissance aircraft, which were given the designation P-40N-6-CU. The P-40N-5-CUs were given serial numbers 42-104829 to 42-105928.

With serial numbers 42-105929 to 42-106028, 100 aircraft of a special winter variant as P-40N-10-CU followed. To achieve faster climbing, two machine guns were again removed.

P-40N-10-CU, 42-106019. Source: Wilco Vermeer collection

With adjustments to the placement of the battery, new landing lights and a larger fuel capacity, a series of 377 P-40N-15-CU aircraft with serial numbers 42-106029 to 42-106405 followed. This version again availed of the original full armament of six machine guns. Here as well, an unknown number of aircraft have been converted into P-40N-16-CU photo reconnaissance aircraft.

Engine development also continued, so that the next series P-40N-20-CU was equipped with an Allison V-1710-99(F22R) engine. This was almost the same as the previous one, but equipped with an automatic control system. No fewer than 1,523 of these were built with serial numbers 42-106406 to 42-106428 and 43-22752 to 43-24251.

The next 500 aircraft with designation P-40N-25-CU had a revised instrument panel and received serial numbers 43-24252 to 43-24751. Self-sealing plastic fuel tanks were also used here for the first time. An equally unknown number of aircraft have been converted into P-40N-26-CU photo reconnaissance aircraft and three aircraft have been equipped with dual controls as trainer RP-40N-26-CU.

After an overhaul of the oil system, the P-40N-30-CU was created. Of these, 500 aircraft were built with serial numbers 44-7001 to 44-7500. 22 of these aircraft have been converted into trainers with dual controls as RP-40N-31-CU.

P-40N-30-CU, 44-7492. Source: Wilco Vermeer collection

With changes to the carburetor, instruments and lighting, the P-40N-35-CU was created, of which another 500 units were built with serial numbers 44-7501 to 44-8000.

The last version ordered, the P-40N-40-CU, would initially consist of 1000 aircraft. Ultimately, only 220 were delivered with serial numbers 44-47749 to 44-47968. The new 1360 hp Allison V-1710-115 was selected as its engine. For the first time, the tail rudders were covered with aluminum instead of linen. Another first was that from aircraft serial number 44-47860 onwards, the P-40 was no longer painted in camouflage colours but retained their aluminum colour. Furthermore, several modernisations had been made to various equipments

When the production line completed the final P-40N, the total number of P-40 aircraft produced reached 13,739.

The Brazilian Air Force received 41 P-40Ns with serial numbers 4020 to 4100, of which 4064 has been preserved as a monument.

On a trial basis, the XP-40N became an aircraft equipped with a bubble cockpit. Examples of the P-40N are preserved in the Cavanaugh Flight Museum in Addison, Texas, the Champlin Fighter Museum in Mesa, Arizona, the Kalamazoo Aviation Museum in Kalamazoo, Michigan, the Museum of Aviation in Georgia, the Pope Air Force Base in North Carolina, and the Air Museum "Planes of Fames" in Chino, California.

The other Allies received the P-40N, which was mainly referred to by the British designation Kittyhawk Mk IV. The Soviet Union alone received 1,791 aircraft, 130 of which were originally intended for the RAF with the original British serial numbers FS270 to FS399. The remainder went mainly to the RAF, RAAF and RNZAF

The RAF was allocated 586 aircraft (of which 130 were re-allocated to the Soviet Union). The remainder were mainly deployed at RAF and RNZAF units in the Far East. The RAF aircraft received serial numbers FT849 to FT954 and FX498 to FX847. They also flew in North Africa with No 112 (Sharkteeth) Squadron.

The Australian RAAF received 79 aircraft as Kittyhawk Mk IV from the USAAF P-40N-1-CU stock, with serial numbers A29-415 to 29-419, A29-435 to A29-442, A29-461 to A29-472, A29-503 to A29-541, A29-559 to A29-563 and A29-577 to A29-587. Subsequently 29 P-40N-5-CU aircraft with serial numbers A29-542 to A29-558 and A29-564 to A29-576, followed by 105 P-40N-20-CU aircraft (A29-600 to A29-704), 22 P-40N-25-CU aircraft (A29-800 to A29-811 and A29-819 to A29-828), 29 P-40N-30-CU aircraft (A29-900 to A29-928), 80 P-40N-35- CU aircraft (A29-1000 to A29-1079) and 122 P-40N-40-CU aircraft (A29-1100 to A29-1221).

67 aircraft with serial numbers C3-500 to C3-566 were purchased especially for the Dutch Nr. 120 NEI Squadron operating with the RAAF. The New Zealand RNZAF received 172 aircraft from the RAF group with serial numbers NZ3120 to NZ3179, NZ3182 to NZ3270 and NZ3272 to NZ3293. The RCAF (Canada) received 35 P-40Ns with serial numbers 846 to 880.

P-40N, No. 120 (NEI) Squadron. Source: NIMH 2157_032255

Five New Zealand P-40Ns have been preserved in various states (from monument to airworthy).

Two P-40K aircraft (42-9987 and 42-45722) and a P-40N (43-24571) were extensively modified as the XP-40Q in an attempt to produce a truly modern fighter based on the P-40. The first one was equipped with a new cooling system, longer nose and a four-blade propeller. The other two were even more intensively modified and equipped with a 1425 hp Allison V-1710-121 engine. This type version would be equipped with six machine guns or 20 mm cannons. However, it could no longer compete with the new P-47 and P-51 types and was therefore not put into production.

XP-40Q-1. Source: Wilco Vermeer collection

The first aircraft, 42-9987 was designated XP-40Q-1 and had the standard P-40 cockpit but a slimmer nose with air intake on top of the engine like the early P-40 types. This aircraft later received a modified cockpit in the form of a drop cockpit and a cooling inlet under the nose, after which it was designated XP-40Q-2.

XP-40Q-2A. Source: Public Domain (unknown)

XP-40Q-3. Source: Public Domain (unknown)

The third aircraft, 43-24571, received modifications to the cockpit canopy and was designated XP-40Q-3.

A total of 600 P-40F and P-40L aircraft were intensively modified. They were equipped with an Allison V-1710-81 engine instead of the Packard-Merlin engine. The P-40Fs were converted into P-40R-1s and the P-40Ls into P-40R-2 training aircraft.

P-40R. Source: Public Domain (unknown)