Curtiss P-40 Warhawk: One of WW II’s Most Famous Fighters

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If the Curtiss P-40 Warhawk was not the best fighter in the arsenal of the U.S. Army Air Corps (USAAC) when the United States entered the conflict, it was the most numerous type available. The Lockheed P-38 Lightning could outperform the P-40, especially at high altitude, but the P-40 was less expensive, easier to build and maintain, and — most important — it was in large-scale production at a critical period in the nation’s history when fighter planes were needed in large numbers.

A total of 11,998 P-40s were built before production was finally terminated in 1944. Warhawks constituted the principal armament of the U.S. Army Air Forces (USAAF) fighter squadrons throughout 1942 and 1943. Even after the appearance of newer types of fighter aircraft in the USAAF rendered the P-40 obsolete, it continued to contribute to victory in a variety of Allied air forces.

The P-40 was the product of a long development process that began when the USAAC invited various aircraft companies to submit designs for its 1935 fighter competition. Curtiss and Boeing had dominated the U.S. Army and Navy fighter plane business since the end of World War I. In 1933, however, Boeing had beaten Curtiss in competition for a lucrative Army fighter contract with its innovative P-26 Peashooter. The P-26 was a monoplane of all-aluminum, stressed skin construction. Ralph Damon, the head of Curtiss, was determined that his company’s next fighter should have the benefits of the latest design and construction technology. In 1934, he hired Donovan R. Berlin as Curtiss’ new chief engineer. Berlin had previously worked at Douglas and Northrop, two firms that had been at the cutting edge of aircraft design.

The four rival designs for the 1935 fighter competition, from Curtiss-Wright, Seversky, Vought and Consolidated, were the first really modern fighters to be evaluated by the Army. All four were low-wing monoplanes of all-metal, stressed-skin construction with retractable landing gear and enclosed cockpits.

Curtiss designated its entry the Model 75. Since all Curtiss fighter aircraft had been called ‘Hawks’ since the mid-1920s, the new fighter became known as the ‘Hawk 75.’ Powered by a 900-hp Wright air-cooled radial engine, the Hawk 75 was first flown in May 1935 and demonstrated good maneuverability and flying characteristics. Initially, however, the USAAC rejected the Hawk 75 in favor of the Seversky P-35. It subsequently reversed that decision, however, and in 1937 it ordered 210 of the Curtiss fighters — the Air Corps’ largest order of a single type of fighter aircraft since the end of World War I. Fitted with a more powerful Pratt and Whitney R-1830 Twin-Wasp radial engine, the new fighter was designated the P-36A.

Significant as the USAAC order was, it was small compared to the total number of Hawk 75s sold overseas. Curtiss had been selling large numbers of Hawk biplane fighters to various nations in Europe, Asia and Latin America since the 1920s. With war clouds gathering throughout the world in the late 1930s, Curtiss had little difficulty finding foreign buyers for its new monoplane.

By far the largest customer for the Curtiss fighters was France. At the time of the 1938 Munich crisis, the French aircraft industry was having difficulty meeting its air force’s demands for modern fighters. The French government decided that the most expedient solution to the problem was to order 730 Hawk 75s from Curtiss, in the neutral United States. H-75As, as the French called them, were the most numerous fighters in the Armée de l’Air’s inventory when WWII began, and they shot down more German planes than any other French fighter aircraft. The Hawk 75s that had not yet been delivered to France before the country surrendered to Germany in June 1940 were transferred to Britain’s Royal Air Force (RAF), which called them Mohawks.

Some of the French H-75As were seized by the Germans after France’s collapse and sold to the Finns for use against the Soviet Union. Others, still in French hands, were transferred to North Africa, where they continued to operate under the control of the Vichy French government. On at least one occasion, during the Allied landings in Morocco in November 1942, Vichy French H-75As tangled unsuccessfully with U.S. Navy Grumman F4F Wildcats.

Since the end of World War I, domination of the world’s aviation engines had been alternating between liquid-cooled in-line engines and air-cooled radial engines. The liquid-cooled engines were generally more powerful, but they were also heavier, more complex and vulnerable to damage if the coolant leaked out. The radial engines were lighter and more compact, but their larger frontal area created aerodynamic drag. As it happened, the Hawk 75 was developed at a time when the liquid-cooled V-12 engine was just beginning to come back into vogue, both in Europe and the United States. The principal reason was the introduction of high-temperature cooling utilizing Glycol rather than water, a development that made it possible to reduce weight and drag by decreasing the size of the cooling radiator by as much as 75 percent.

In February 1937, while the USAAC was still evaluating the P-36 for production, it contracted with Curtiss to re-engineer the fighter to test the potential of a highly promising new liquid-cooled V-12 engine, the turbosupercharged General Motors Allison V-1710. To save money, the factory rebuilt the original Hawk 75 prototype to create the new prototype. First flown in 1937, the XP-37, as the new fighter was called, was not an unqualified success. Although its 1,150-hp Allison engine and aerodynamic lines gave it far better performance than the P-36, it had a number of serious drawbacks as a combat plane. The General Electric turbosupercharger boosted the engine’s critical operating altitude — i.e., the altitude at which the supercharger would operate at peak efficiency — to 20,000 feet, but it proved unreliable and likely to catch fire. In addition, the cockpit had to be moved aft to balance the heavy engine and its bulky turbosupercharger, which reduced pilot visibility.

Despite the promising performance of the turbosupercharged Allison engine, the problems encountered with the XP-37 were rapidly reducing the likelihood that the airplane ever would be placed in production. Therefore, Don Berlin decided to take a different approach to a P-36 derivative equipped with an Allison engine. On March 3, 1938, Curtiss submitted a proposal to the Air Corps to modify a P-36 airframe to accept an Allison engine fitted with a mechanically driven supercharger. The modifications to the airframe were less extreme than those required for the XP-37, as they did not require moving the cockpit aft. The engine also proved to be more reliable than the turbosupercharged Allison used in the XP-37, although its critical operating altitude was reduced to 10,000 feet, with performance falling off at higher altitudes up to its service ceiling of 32,750 feet. At Curtiss the new fighter design was known as the Model 81, but the Air Corps called it the XP-40.

The prototype XP-40 was first flown on October 14, 1938, only two weeks after the settlement of the Munich crisis bought the world a one-year reprieve from war. It was modified from the 10th production P-36A airframe. The XP-40’s sharply pointed nose was longer than that of the P-36, though not so long as that of the XP-37. Since the cockpit was not displaced aft, the pilot’s view was better than in the XP-37. The radiator, which had been buried in the fuselage between the engine and cockpit of the XP-37, was now installed under the fuselage, aft of the wings.

Although Curtiss had guaranteed that the XP-40 would achieve 360 mph, the prototype was not immediately able to do so. After a series of modifications that took several more months, however, the fighter demonstrated a top speed of 366 mph at 15,000 feet. The most conspicuous change was the relocation of the radiator to a new position under the nose, giving the P-40 its most characteristic feature.

The XP-40 won the Army’s 1939 fighter competition against the Lockheed XP-38 Lightning, Bell XP-39 Airacobra, Republic AP-4, and Curtiss’ own XP-37 and Hawk 75R, the latter a turbosupercharged version of the radial-engine P-36. The XP-38 outperformed the XP-40, especially at high altitudes, and was more heavily armed, but the XP-40 had the advantage of being based on an existing fighter design that was already on the production line. That meant that Curtiss could put the P-40 into production with a minimum of delay, and at the highly competitive price of $24,566.60 apiece. On April 26, 1939, Curtiss was awarded a contract for 524 P-40s — once again, the largest order for fighter planes placed by the Army since 1918.

The P-40 prototype was armed with one .50- and one .30-caliber machine gun — the standard USAAC fighter armament during the 1930s — but the production model was armed with two .50-caliber machine guns. In keeping with President Franklin D. Roosevelt’s policy of making the latest American military hardware available to the Allies, 140 of the original batch of P-40s were diverted to France. They were armed with one .50-caliber machine gun in the fuselage and four 7.5mm guns in the wings. None of those P-40s were delivered by the time France capitulated, however. Instead, the export P-40s were delivered to the RAF and became known as Tomahawk Mk.Is.

The British were grateful for all the combat aircraft they could get in 1940, but they did not regard the Tomahawk Mk.I as suitable for combat. Many of the Tomahawk Mk.Is still had metric instruments and other French equipment that were not compatible with RAF service, and their French throttle control levers worked in reverse of the way British or American ones did. More important, they lacked self-sealing fuel tanks and had neither armor nor bulletproof windscreens to protect their pilots. Consequently, the Tomahawk Mk.Is were relegated to tactical reconnaissance duties.

As a result of European combat experience, Curtiss installed armor in the P-40 and increased its armament, adding a .30-caliber machine gun in each wing. The improved fighters were called P-40Bs by the Americans and Tomahawk Mk.IIs by the British. The next model, known as the P-40C, also had self-sealing fuel tanks and yet another .30-caliber machine gun in each wing. The USAAC ordered a total of 324 P-40Bs and P-40Cs during 1941. At the same time, the British ordered 930 P-40Cs. Those with British radio equipment were called Tomahawk Mk.IIas, while the ones delivered to the RAF with American radios were designated Tomahawk Mk.IIbs.

First flown in April 1941, the P-40C was considered the first truly combat-ready version of the P-40 line. A price had been paid for the necessary improvements, however. The aircraft’s gross weight had increased from 7,215 to 8,058 pounds, an increase of 843 pounds or approximately 11 percent, with no increase in engine power. The P-40C’s rate of climb suffered, it was less maneuverable, and its maximum speed fell to 340 mph. By comparison, the Messerschmitt Me-109E used by the Luftwaffe in 1941 weighed only 6,100 pounds and had a top speed of 360 mph. Air Chief Marshal Sir Kenneth Cross, who served in the RAF’s Desert Air Force, recalled that ‘the Tomahawk was beautifully built, but…short on performance compared to the (Messerschmitt) 109F and G.’

By the end of 1941 the USAAC had deployed P-40s overseas. Thirty were flown to Iceland from the aircraft carrier Wasp, and 99 of them were stationed in Hawaii. In addition, four squadrons of P-40s were deployed in the Philippines. It was with the British that the Tomahawk Mk.IIs first saw action, however, flying reconnaissance sorties and fighter sweeps across the English Channel with the RAF and Royal Canadian Air Force (RCAF) in 1941. By May 1941 Tomahawks were also operating in the Middle East, eventually serving in that theater with Australian and South African fighter squadrons as well as the RAF. In addition, the British sent 195 Tomahawks to the Soviet Union after the Germans invaded that country on June 22, 1941.

The first serious use of the P-40 as a fighter occurred when Iraqi forces led by Rashid Ali El-Ghailani rose against the British in Iraq on May 2, 1941. When the Germans and Italians sent aircraft to assist the revolt, staging from Vichy French bases in Lebanon and Syria, the British sent three Bristol Blenheims to bomb the air base at Palmyra on May 14, escorted by two Tomahawks of No. 250 Squadron, RAF, flown by Flying Officers G.A. Wolsey and F.J.S. Aldridge. The Iraqi revolt was crushed by May 30, but the British decided that Vichy France’s violation of neutrality justified the invasion and occupation of Lebanon and Syria. Tomahawks of No. 3 Squadron, Royal Australian Air Force (RAAF), took part in the first attack on June 8, helping to destroy a Dewoitine D.520 fighter and damage three others at Rayak airfield. Elsewhere on that same day, two of No. 250 Squadron’s Tomahawks drew first blood for the P-40 in the air when they shot down an Italian Cant Z.1007bis reconnaissance plane five miles northwest of Alexandria, Egypt. The Vichy French put up a spirited fight before finally signing an armistice on July 14, but the Tomahawks of No. 3 Squadron RAAF also acquitted themselves well, holding their own against France’s top-of-the-line D.520s and shooting down two out of eight German Junkers Ju-88As of II Gruppe, Lehrgeschwader 1, operating from Crete, that tried to interfere with British landings on the Levantine coast on June 12.

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Tags: 20th - 21st Century, Airborne Operations, Aircraft, Aviation History, Historical Conflicts, World War II