Curtiss XP-40

Last revised December 26, 1999

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 at the time 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. Strangely enough, the P-40 continued in production long after later and more modern types were readily available, the numbers manufactured reaching the third highest total of American World War II fighters, after the Republic P-47 and the North American P-51.

The P-40 was already obsolete by European standards even before the first prototype flew, and it never did catch up. Its initial inadequacies, in the form of low firepower and lack of self-sealing fuel tanks or armor, were a reflection of mid-'thirties USAAC requirements. The P-40 had been developed basically as 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. Low-altitude performance and rugged construction received priority over high-altitude capabilities. The military doctrine of the "ascendancy of bombardment over pursuit" was dominant in 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 main tasks for any future fighter aircraft.

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 and far more capable 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!

A total of 13,739 Curtiss P-40s were built, which included the Tomahawks and Kittyhawks built for export as well as the P-40s built for the USAAF.

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, in which the P-36 design was reworked to incorporate the Allison V-1710 liquid cooled V-type engine. 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.

There had to be a considerable amount of replumbing to adapt the P-36 airframe to the liquid-cooled Allison. The carburetor intake for the single-stage supercharger was installed in the upper nose, between the two nose guns. An oil cooler was mounted underneath the nose, and the radiator was located in a ventral position just aft of the wing. Unlike in the XP-37, the cockpit remained in the same location as in the P-36.

The XP-40 flew for the first time on October 14, 1938, with test pilot 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.

Early flight trials were disappointing, the arcraft top speed being barely 300 mph. 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 as well as 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.


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

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

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

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

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

  6. Hawk Dynasty: The Curtiss Hawk Monoplanes, Part 2, Ken Wixey, Air Enthusiast No 72 (1997).

  7. e-mail from Daniel Stover on P-40 production counts