The Curtiss P-36 was the first of the new generation of monoplane fighters to enter service with the USAAC. It was a contemporary of the Supermarine Spitfire, the Hawker Hurricane, and the Messerschmitt Bf 109, all of which were introduced within a few months of each other in the mid 1930s. Even though the P-36 owed very little to previous Curtiss biplane pursuits, the name *Hawk* was still generally applied to the aircraft.
The P-36 pursuit had its origin in the Model 75 project which was originally developed as the Curtiss entry in the US Army pursuit aircraft competition scheduled for May 1935. Curtiss lost the initial contest but was the real winner in the end, with 227 examples sold to the USAAC, 753 exported, and at least 25 built under license in other countries.
The Model 75 owed relatively little to previous Curtiss designs. The principal designer was Donovan A. Berlin, who had come over to Curtiss from Northrop, and the structure was heavily influenced by earlier Northrop designs. The prototype carried the civilian registration of X-17Y. It was an all-metal low-wing monoplane, with the metal-frame moveable control surfaces being fabric covered. The cockpit was enclosed by a sliding canopy, with the canopy being faired into a high rear turtledeck. Both the main undercarriage units and the tailwheel retracted, the main legs rotating backward 90 degrees and turning 90 degrees on their axes simultaneously to lay the wheels flat in the thin rear portion of the wing. This retraction mechanism had originally been developed by Boeing, which received a royalty whenever any other aircraft manufacturer used it. The wing was built in two halves joined on the aircraft's centerline. Portions of the outer wing structure were sealed to provide flotation in case of a forced landing in water. Hydraulically-actuated split flaps were fitted to the trailing edge of the wing. Initial armament was the standard US fighter armament of the time--one 0.30-in and one 0.50-in machine guns under the forward fuselage deck, firing through openings in the top of the cowling. No armor protection or self-sealing fuel tanks were fitted.
Prototype construction began in November 1934. Initially, the aircraft was powered by the unfortunate 900 hp Wright XR-1670-5 (SCR-1670-G5) twin-row air-cooled radial. The first flight of the Model 75 took place in May of 1935. During early tests, the prototype had demonstrated a maximum speed of 281 mph at 10,000 feet, a service ceiling of 30,000 feet, and a range of 537 miles. Weights were 3760 lbs empty, 4843 lbs gross. Length was 28 feet 3 1/2 inches, wingspan was 37 feet 0 inches, and wing area was 237 square feet.
On May 27, 1935, Curtiss submitted the Model 75 to the USAAC Material Division's single seat fighter competition which was to be held at Wright Field that very month. However, the Model 75 was the only competitor ready in time for the scheduled flyoff. The primary competitor, the two-seat Seversky SEV-2XP, had been "heavily damaged" during delivery to Wright Field, and did not arrive there until June 18. The SEV-2XP was soon returned to the Seversky factory where it was reworked into a single seater with retractable undercarriage. The competition was delayed until the SEV-1XP could be ready.
It finally arrived at Wright Field on August 15, bearing the designation SEV-1XP. The only other serious competitor, the Northrop 2A had taken off on its maiden flight on July 30, headed out over the Pacific, and promptly disappeared into thin air.
Curtiss protested that this delay had given the Seversky competitor an unfair advantage, and convinced the Army that it should defer its decision until after a further competitive evaluation which was to take place in April of 1936. During the early flight tests, the XR-1670-5 engine which powered the Model 75 had proven itself to be totally unsatisfactory. Don Berlin took the opportunity afforded by the delay to replace this engine by a 700 hp Pratt & Whitney R-1535.
Since this engine model had passed its peak of development, a nine-cylinder single-row Wright XR-1820-39 (G5) Cyclone radial was quickly substituted. This engine was rated at 950 hp for takeoff and at 850 hp normal maximum output. With this engine, the prototype was designated Model 75B (Model 75A had been reserved for the export version of the Hawk). In its final form, the Model 75B had a strengthened cockpit canopy and introduced a scalloped aft fuselage decking behind the cockpit for a somewhat improved rear view.
The new Cyclone radial of the Model 75B proved to be almost as unsatisfactory as its R-1670 predecessor, and failed to deliver its full rated power. There were no fewer than four engine changes during the Wright Field trials. In addition, there were problems with incompatibility between the engine and the airframe. The Model 75B proved capable of attaining only 285 mph (versus the 294 mph at 10,000 feet guaranteed by Curtiss-Wright). Even though the Seversky entry also fell short on promised performance and in addition was more expensive than the Curtiss entry, the Model 75B lost out to the Seversky competitor, which won an order for 77 examples under the designation P-35.
Even though the prototype Model 75 never became Army property, some sources refer to the various configurations of this aircraft under the collective designation "XP-36". This was a matter of historical convenience only, since there never was any such official designation. The original configuration of the Model 75 prototype with the 900 hp Wright SCR-1670-G5 radial was given the retroactive company designation of Model 75D. The prototype aircraft was later rebuilt and delivered to the Army as the XP-37, of which more in a later installment.
On June 16, 1936, Curtiss got a consolation order from the Material Division for three examples of the Model 75B under the designation Y1P-36, perhaps because the USAAC was getting nervous about the inability of Seversky to meet its delivery schedules and was therefore hedging its bets. Serial numbers of the Y1P-36s were 37-68/70, and the company designation for these planes was Model 75E. At Army direction, they were to be powered with the Pratt & Whitney R-1830-13 Twin Wasp radial, virtually the same type of engine that was used by the P-35.
The Twin Wasp was rated at 900 hp at 2550 rpm at 12,000 feet, having been de-rated from 1050 to 950 hp for takeoff. The engine drove a hydraulically-operated, constant-speed three-bladed Hamilton Standard propeller. Armament was the Army standard of the day, one 0.30-inch and one 0.50-inch machine gun under the cowling and synchronized to fire through the propeller arc. The Y1P-36 could be distinguished from the prototype by the R-1830 engine and also by the presence of modified and larger view scallops behind the cockpit.
The first Y1P-36 was delivered to the Army in March of 1937, and was tested at Wright Field in June of that year. The Wright Field test pilots were uniformly enthusiastic about the new Curtiss plane, commenting favorably about its maneuverability. The effectiveness and operation of all controls throughout the speed range of the fighter were excellent, and stability and ground handling were quite favorably rated.
However, there was some criticism of the location of the undercarriage and flap controls, some complaints about the cabin ventilation, and some unfavorable comments about the curvature of the windshield which resulted in some distortion of vision during landing. With the R-1830 engine, the Y1P-36 did so well that it won a 1937 Army competition, and on July 7, 1937, the Army ordered 210 P-36As, the largest single US military aircraft order since the First World War. Curtiss's private venture had finally paid off.
Serials of the P-36As were 38-1/210. The principal difference between the P-36A and the Y1P-36 was the addition of engine cowl flaps and the addition of bulging "frog's eye" covers over the machine gun ports in the engine cowling. The P-36A had a fully-rated 1050 hp Pratt & Whitney R-1830-13 Twin Wasp engine driving a Curtiss Electric constant speed propeller. Empyt and normal loaded weights were 4567 lb and 5470 lbs. Maximum speed was 300 mph at 10,000 feet. Normal range was 825 miles. Initial climb rate was 3400 feet/minute. An altitude of 15,000 feet could be attained in 4.8 minutes, and service ceiling was 33,000 feet.
Before completion, P-36A Ser No 38-10 was converted to the XP-40 (Model 75P) and 38-4 became the XP-42 (Model 75S). More of both of these later in the series!
P-36A Ser No 38-020 was flown in November 1938 with an R-1830-25 engine offering 1100 hp for takeoff. This airplane was redesignated P-36B. It attained a maximum speed of 313 mph. The airplane was subsequently converted back to P-36A standards.
The P-36A had always been underarmed in comparison with contemporary foreign fighters (e. g. the Spitfire and Hurricane), and P-36A Ser No 38-085 had undergone an experiment in which the fuselage guns were supplemented by the addition of a 0.30-in machine gun in each outer wing panel. This installation was successful, and it was adopted for the last 30 aircraft in the original order (Ser Nos 38-181/210). They were redesignated P-36C. The P-36C also featured an R-1830-17 (S1C3-G) engine rated at 1200 hp for takeoff. These changes had been ordered on January 16, 1939, and the P-36C could be distinguished from the P-36A by the addition of cartridge case retainer boxes protruding underneath the wings. Despite the extra drag produced by the underwing cartridge boxes and the increased weight, the increased power of the engine raised the maximum speed of the P-36C to 311 mph, although the range was lowered to 600 miles. Service ceiling was 33,700 feet. Weights were 4620 lbs empty, 5734 lbs loaded. Wing span was 37 feet 4 inches, length was 28 feet 6 inches, and wing area was 236 square feet.
P-36A Ser No 38-174 was withdrawn from squadron service early in 1939 and fitted with four belt-fed 0.30-in machine guns in the wings. At the same time, the fuselage mounted armament was changed to a pair of 0.5-in machine guns. Thus armed, the modified aircraft was redesignated XP-36D.
P-36A Ser No 38-147 was fitted with new outer wing panels each housing FOUR 0.30-in machine guns (a la Spitfire and Hurricane). The fuselage-mounted 0.50-in gun was retained but rendered inoperable. As such, the aircraft was redesignated XP-36E. The XP-36E was retired to an Army mechanics' school in August of 1943.
The XP-36F was created by taking P-36A Ser No 38-172 and fitting it with two 23-mm Danish-built Madsen cannon in underwing fairings. The standard P-36A fuselage armament was retained. Unfortunately, this additional armament caused the maximum weight to rise to 6850 pounds and the maximum speed to fall to 265 mph. Consequently, the experimental armament was soon removed and the airplane reverted to a standard P-36A. It was surveyed in October 1944.
The first Y1P-36 (Ser No 37-068) was briefly tested with two twin-bladed contrarotating propellers, the first such installation on an American aircraft.
Model 75A was the company designation for a Curtiss-owned demonstrator which carried a civilian registration of NX22028. This demonstrator aircraft was used to carry out several company-originated experiments. First, it was fitted with an external mechanical supercharger mounted underneath its Pratt & Whitney R-1830 engine and briefly designated Model 75J. Then, it was experimentally fitted with a turbosupercharged R-1830-SC2-G engine. The supercharger was fitted underneath the nose just aft of the engine cowling, and the intercooler was mounted underneath the trailing edge of the wing.
The company designation for this modification was Model 75R. Empty and normal loaded weights went up to 5074 lbs and 6163 lbs. During trials in January 1939, it attained a maximum speed of 330 mph at 15,000 feet. However, the poor reliability and complexity of the turbosupercharger led the USAAC to decide not to proceed with a supercharged variant of the P-36, choosing instead to purchase the turbo-supercharged Seversky (Republic) XP-41, which had been converted from the last P-35. After trials at Wright Field, the aircraft was returned to the Curtiss plant in Buffalo, where it was fitted with a Wright R-1820 engine and resumed its role as a demonstrator.
The first production P-36A was delivered to Wright Field in April of 1938. The 20th Pursuit Group at Barksdale Field, comprising the 55th, 77th, and 79th Pursuit Squadrons, had been designated as the first recipients of the new Curtiss fighter, and they had relinquished their Boeing P-26 in anticipation of the deliveries. However, the new Curtiss fighters began to encounter an extensive series of teething troubles almost as soon as they reached the field.
Severe skin buckling in the vicinity of the landing gear wells had appeared, dictating increased skin thicknesses and reinforcing webs. Engine exhaust difficulties and some weaknesses in the fuselage structure were also encountered. Despite both production line and field fixes, the P-36As were grounded again and again. At one time, the 20th Pursuit Group was down to six serviceable P-36As, and even these planes had to be flown under severe limitations on their speed, aerobatics, and combat maneuvers.
The 1st Pursuit Group at Selfridge Field, Michigan, consisting of the 17th, 27th, and 94th Pursuit Squadrons, had also been scheduled in 1938 for conversion to the P-36A. However, this Group was forced to await the efforts being made at Buffalo to wring out the new fighter's problems. In the event, only the 94th Squadron got any P-36As during 1938, operating them along Seversky P-35s. The 27th Squadron received a few P-36As during early 1939, but neither the 27th nor the 94th Squadron ever got a full complement of P-36As, the balance being made up by Seversky P-35s. The 17th Squadron never got ANY P-36s, their strength being made up solely of P-35s.
In 1939, the 33rd, 35th, and 36th Squadrons of the 8th Pursuit Group at Langley Field, Virginia were equipped with P-36s.
By early 1941, the P-36 was recognized as being obsolescent, and had been largely supplanted in first-line Army Air Force (as the Army Air Corps had been renamed) units by such aircraft as the Bell P-39 Airacobra, the Lockheed P-38 Lightning, and the Curtiss P-40. At home, the P-36s were largely relegated to training units. By the time of Pearl Harbor, P-36s were serving with the 35th Training Group based at Moffett Field, California and with the 36th Training Group based at Langley Field, Virginia. These outfits trained with the P-36 before they converted to more modern fighters.
Other P-36s were transferred overseas. P-36s served with the 24th, 29th, and 43rd Squadrons of the 16th Pursuit Group and with the 51st, 52nd and 53rd Squadrons of the 32nd Pursuit Group, both groups being based at Albrook Field in the Canal Zone, where they flew alongside the now totally-obsolete Boeing P-26. During February of 1941, 20 crated P-36s were delivered to Alaska, and these planes served with the 23rd Squadron at Elmendorf Field in Alaska. At about the same time, 31 P-36s arrived in Hawaii from San Diego aboard the carrier *Enterprise*. These fighters entered service with the 78th Squadron of the 18th Pursuit Group and with the 46th and 47th Squadrons of the 15th Pursuit Groups, all being based at Wheeler Field, Hawaii.
At the time of the Pearl Harbor attack, 14 P-26As, 39 P-36As and 99 P-40s comprised the air defense of the islands. Most of these aircraft were destroyed or damaged on the ground, but four P-36As of the 46th Squadron managed to take off and attack a formation of nine Nakajima B5N1 torpedo bombers on the second wave. Two of the Najajimas were shot down, gaining the first USAAF "kills" of the Pacific War.
After Pearl Harbor, there was no other combat while in US service. P-36s were quickly withdrawn from combat outfits and relegated to training units. Ten P-36As (serials 38-39, 43, 51, 53, 54, 60, 106, 158, 159, and 175 were transferred to Brazil in March of 1942.
The Norwegian government had issued an order for 36 Hawk 75A-8 export versions of the P-36 just before the German occupation, and when these aircraft were completed, they were impounded by the US government. Six were delivered to Free Norwegian forces in Canada in February 1941, where they were operated as fighter trainers by the "Little Norway" training establishment near Toronto. The rest of the A-8s were requisitioned by the US Army as P-36G.
These aircraft received serial numbers 42-36305/36322 and 42-108995/109006. These aircraft were powered by the export-model 1200 hp Wright R-1820-G205A Cyclone radial, which was redesignated R-1820-95 by the Army. Since these aircraft were considered useless as combat types and in addition were incompatible with other P-36s because of their Wright engines, the P-36Gs were sent to Peru under Lend-Lease in 1943. One survives in the Peruvian Air Force Museum.
There is a P-36A on display at the Wright Patterson Air Force Base Museum in Dayton, Ohio. I am unaware of the service history of this particular airplane.
Sources:
Curtiss Aircraft, 1907-1947, Peter M Bowers, Naval Institute Press,
1979
The Curtiss Hawk 75, Aircraft in Profile No. 80, Profile
Publications, Ltd. 1966
War Planes of the Second World War, Fighters, Volume Four, William
Green, Doubleday, 1961.
Air Enthusiast, Volume 1, William Green et al, Doubleday, 1971.
Joe Baugher
AT&T Bell Laboratories
2000 North Naperville Road
Naperville, Illinois 60566-7033.
