The Hawk Takes Flight

The Curtiss P-40 Hawks

by Randy Wilson

Copyright © 1996 by the Confederate Air Force and Randy Wilson. All rights reserved.

I wish I had a dollar for every time I have been on an air show ramp and heard a young voice cry out, "Hey — look, Dad. It’s a Flying Tiger!"

Probably no other World War II plane is as closely identified with the men who flew it in combat than the Curtiss P-40. However, after the P-40 entered combat, many called it "second-rate" and spoke of its poor performance relative to opposing enemy fighters. While it is true that the P-40 rarely out-performed enemy fighters, it did prove to be a rugged workhorse, which when well-flown, rewarded its pilot with success and a safe journey home.

The Curtiss Aeroplane Division of the Curtiss-Wright Corporation stemmed from the 1929 merger of two long-time rivals in American aviation — the Wright brothers and Glenn Curtiss, or rather, the companies that each had originally founded. The Wright Aeronautical Corporation had become primarily an engine manufacturer, and continued this specialization after the merger, while the former Curtiss Aeroplane and Motor Company concentrated on designing and building aircraft. After 1929, most engines produced by the new company were known as Wrights, while most aircraft were given the Curtiss name, with a few exceptions.

In the early 1920s, the domination of the U.S. air racing scene by Curtiss designs led to the company’s first production fighter, or pursuit aircraft as they were then known, the PW-8. Powered by the 440 hp Curtiss D-12 water-cooled engine (thus the PW, Pursuit Watercooled designation), this open-cockpit biplane first flew in January of 1923, and was the genesis of the Curtiss Hawk line.

The trademarked name "Hawk" was first applied to the 1926 Army Air Corps version of the PW-8, redesignated as the P-1. Variations of the basic Hawk biplane continued to be developed in the

late 1920s, a few powered by air-cooled radial engines, but most with Curtiss liquid-cooled power-plants. The prototype of a new Hawk biplane was entered in the 1927 National Air Races, powered by a new 600 hp Curtiss V-1570 Conqueror V-12 engine. The XP-6A averaged 201 mph, and was the first U.S. Army Air Corps plane to break the 200 mph barrier. The Army ordered the P-6 into production in 1928.

The P-6E Hawk was the final U.S. production version of the biplane Hawks, with delivery beginning in late 1930. Powered by a 600 hp Conqueror engine, it had a top speed of 198 mph and was armed with two .30 caliber machine guns.

By 1931, the Army Air Corps recognized the increased development of the monoplane fighter in Europe, and called for new designs to be delivered in the 1933-36 period. Curtiss built the XP-31 Swift, a wire-braced monoplane with spatted fixed gear, powered by either a Wright Cyclone radial or Curtiss Conqueror V-12 engine. This design, however, lost out to rival Boeing’s P-26 "Peashooter."

In mid-1934, a disagreement between John Northrop of Northrop Aircraft Corporation, and his chief engineer Don Berlin, resulted in Berlin’s going to work for Curtiss-Wright. This in turn, resulted in the design of the Curtiss Model 75, the first of the monoplane Curtiss Hawks. The Model 75 featured an enclosed cockpit and fully retracting landing gear. Its original Wright R- 1535 engine, however proved unsatisfactory and was replaced with a Wright XR-1820 of 850 hp for an Air Corps competition for a new fighter in early 1936. A Seversky design won, and was subsequently designated P-35, while Curtiss got an order for three reengined Model 75s, designated Y1P-36s. In 1937, the P-36 won an order for 210 aircraft from the Army Air Corps, plus another 200 for export to France, where the threat of German expansion threatened another World War.

In early 1938, deliveries of P-36As powered by 1,050 hp Pratt & Whitney R-1830 radial engines were initiated to the Army. Later that year, Curtiss began delivery of more export versions of the Hawk 75 to France. However, after France’s defeat in June 1940, many of the aircraft were diverted to Great Britain, where they were designated Mohawks.

Despite the relative success of the P-36, Curtiss and the Air Corps were still seeking a 300 mph plus fighter. By the late 1930s, the science of aerodynamics was being tested on everything from trains to automobiles, but it was in combat aircraft that the relation between power, drag and speed seemed most critical. Thus, the replacement of the bulky air-cooled radial engine with a smoothly-cowled liquid cooled inline engine seemed an obvious way to boost the speed of the Hawk airframe.

Designer Don Berlin suggested mounting an Allison V-1710 in a P-36. Wind tunnel tests suggested a possible top speed of 350 mph at 10,000 feet. In July 1938 the Air Corps issued a contract to modify the 10th production P-36A airframe as the XP-40, using the Allison engine.

The XP-40 made its first flight on Oct.14, 1938, and with a few modifications entered and won the Army’s fighter competition in January 1939. Curtiss was awarded a contract for 524 P-40s in April of 1939. Curtiss gave the P-40 the company model designation H-81, or Hawk 81. Armament was two .50 caliber guns in the nose and a .30 caliber gun in each wing.

Of the initial order, only 200 P-40s went to the USAAC — the Army allowed Curtiss to use the

remaining 324 to fill orders from France and Great Britain. Again, the fall of France resulted in the British taking over the French order, even though the P-40s lacked essential combat equipment and were fitted with French instruments and guns. These early P-40s were called Tomahawks by the British.

By 1940, Rolls-Royce had greatly improved its mechanical superchargers and was introducing two-stage blowers into its newer Merlins, giving British Spitfires and Hurricanes much greater power above 15,000 feet. The Allison’s single-stage supercharger, on the other hand, caused the Tomahawks’ performance to drop off sharply above 12,000 feet. Thus they were primarily used for training and close support, or in theaters such as North Africa, where they often opposed less modern opponents.

In January of 1941, Curtiss began delivery of 131 model H-81-A2s to the USAAC as P-40Bs. Another .30 caliber machine gun was added in each wing as well as provisions for carrying small bombs underwing. Great Britain purchased 110 as Tomahawk IIs, with some eventually going to the Soviet Union and Canada.

Externally, the P-40C, Curtiss model H81-A3, was nearly identical to the P-40B, but had an improved fuel system with better protection and greater capacity, including provisions for a 52 gallon center-line drop tank. The Air Corps received 193 P-40Cs while 930 modified for export were ordered by Great Britain. Of the British order, 195 were diverted to Russia and 100 sold to China, where they became the initial mounts of the American Volunteer Group (AVG), or Flying Tigers.

The exact designation of the Curtiss fighters initially supplied to China and flown by the AVG has been a point of confusion and even debate in many books and articles about the famed Flying Tigers. Those who were fortunate to have flown P-40s before resigning their U.S. military commissions to join the AVG, had probably flown P-40Bs. However, the modifications requested by the British for the H-81-3 model that they ordered and from which the Chinese aircraft were diverted and then further modified, resulted in a P-40 somewhere between a USAAC P-40B and P-40C.

When Lt. R. T. Smith joined the AVG in mid-1941, he had never even flown a fighter, having been an instructor in BT-9s in the Air Corps, yet he became a respected Flying Tiger ace. In his book "Tale of a Tiger," Smith answers the questions about the P-40s he initially flew as follows:

"Perhaps I should mention that most reference to the Tomahawks that we flew identified them as P-40Bs, and in fact that is the model designation that we ourselves used. However, the purists in the aviation fraternity who concern themselves with such things insist that ours more properly should be called P-40Cs. While they had started out as B models, there had been enough changes made in the 100 planes received by the AVG, particularly in fuel cells, communications equipment, and armament, to warrant their being known as ‘Cs. I tend to go along with the experts for a change."

When Japan attacked U.S. bases in Hawaii and the Philippines on Dec. 7,1941, a few P-40Bs and Cs were the most modern fighters on hand to meet the attack.

When the P-40D made its test flight in May 1940, it incorporated significant changes to the shape of the aircraft nose, with an enlarged cooling scoop, and slimmer upper decking, resulting from the removal of the two .50 caliber guns to the wings. A modified hydraulic system included hydraulic chargers for the guns, remedying problems with manual and pneumatic gun chargers that plagued earlier versions. These and other changes resulted in a new Curtiss model number H-87A. Only about 23 P-40Ds were delivered to the USAAC, but about 540 were purchased by Britain as Kittyhawk Is.

The P-40E was similar to the D model, but mounted six .50 caliber guns. Over 800 saw service with the Air Corps, while the British purchased 1,500 similar Kittyhawk IAs. Thirty P-40Es were provided to the AVG in China in March 1942, while other E models saw harsh service with the 343 Fighter Group in the Aleutian Islands.

In mid-1941, a P-40D was fitted with a 1,300 hp Merlin 28 engine. The subsequent increase in performance, over 360 mph at 20,000 feet, resulted in the production of 1,311 P-40F Warhawks and British Kittyhawk IIs, beginning in January 1942. Later F models had a lengthened fuselage to improve directional stability.

The P-40K was basically a refinement of the P-40E, retaining the Allison engine, although rated up to 1,325 hp. Deliveries of 1,300 began in August 1942, and later Ks had the lengthened fuselage introduced in late P-40Fs.

"Gypsy Rose Lee" was one nickname for the Merlin-powered P-40L, as it was basically an F model stripped of two guns, some armor and fuel to try and improve its performance. The 250 pounds lost resulted in only a four to five mph increase in top speed. Six hundred were delivered to the USAAF and 100 to Britain as Kittyhawk IIs (the same designation as British P-40Fs).

Six hundred Allison powered P-40Ms were produced in early 1943, many going to British and Commonwealth air forces as Kittyhawk IIIs and IVs, including one South African Air Force squadron based in Italy.

The largest production series of P-40s began in March 1943, as P-40N Warhawks and British Kittyhawk IVs. Early versions varied in armament and armor, but the majority mounted six .50 caliber machine guns and could carry up to 1,500 pounds of bombs for close support and ground attack missions. P-40Ns were provided to several Allied countries, including Russia and Brazil. About 23 were also modified as two-seat dual control trainers.

Although some P-40F and Ls were redesignated P-40Rs after being reengined with Allisons in place of scarce Merlins, the last in the development of the Warhawk line were the three XP-40Qs. The P-40Qs were drastically rebuilt from K and N models, with extensive aerodynamic clean up, a full bubble canopy, and 1,425 hp Allison with dual-stage supercharger, giving a top speed of 422 mph. However, since this was no better than the contemporary P-51s and P-47s of the time, the P-40Q never saw production.

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