The Hawk 75 was the first modern monoplane fighter to be designed by Curtiss, coming after a long series of successful Hawk biplanes. It entered American service as the P-36, the first modern monoplane fighter to be used in large numbers by the Army Air Corps, but it earned most fame with the French Armée de l'Air, where as the Hawk 75 it was the most successful fighter during the Battle of France. It would later evolve into the P-40 Warhawk, which remained in use throughout the Second World War.
The Curtiss Model 75 was developed by Donovan A. Berlin, a former Northrop designer, and had more in common with earlier Northrop aircraft than with any previous Curtiss design. It was an all-metal low-wing monoplane, with a fully retractable undercarriage - all three wheels retracted, with the main wheels rotating through ninety degrees on their axis and then folding back into the rear of the wing. The aircraft was powered by a radial engine, starting with an experimental Wright engine.
The Model 75 was designed for an Army Pursuit competition scheduled for May 1935. At this point it was powered by the new Wright R-1670 twin-row 14 cylinder radial engine, rated at 900hp. This version of the aircraft was ready for the May 1935 deadline, but its competitors were not, and so the contest was postponed to August 1935. By August it was clear that more work was needed, and the contest post postponed again, this time to April 1936.
The Model 75 was competing against designs from Seversky, Chance Vought and Consolidated. The Seversky design, which eventually won the contest, was a fighter version of their Amphibian of 1933. Chance Vought produced an improved version of the Northrop 3A and Consolidated a single-seat version of their two-seat PB-2A fighter.
One of the main problems with the Hawk 75 was its engine. The original Wright engine was temporarily replaced with a 700hp Pratt & Whitney R-1535, and then by a 675hp Wright R-1820F Cyclone. This version of the aircraft was given the designation Model 75B, and was entered in the April 1936 contest.
In April 1936 Curtiss lost out to Seversky, who won a contract to build 77 of their aircraft as the P-35. A few months later Curtiss also received a production contract, for three Y1P-36 pre-production aircraft (Curtiss Model H75E), to be powered by the 1,050hp Pratt & Whitney R-1830-13 engine. The first of these aircraft was delivered in March 1937, and they won that year's fighter competition. Curtiss was rewarded with an order for 210 P-36As, the biggest American military aircraft order since the First World War.
Curtiss Model Letters
H75A: Export version with a retractable undercarriage
75B: The 850hp Wright Cyclone powered prototype of the April 1936 contest.
75D: A retrospective designation given to the prototype in its first configuration.
74E: The Y1P-36 pre-production aircraft
75H: Simplified version with a non-retractable undercarriage, for the export market
75I: Curtiss designation for the P-37
75J: A Model 75A demonstrator, NX-22028 c/n 12931 when given an external supercharger.
75K: A study for a version to be powered by a 910hp Pratt & Whitney Twin Hornet engine
75L: The P-36A to P-36F
75M: Fixed undercarriage aircraft built in China.
H75N: Export version sold to Thailand
H75O: Export version sold to Argentina
75P: Re-engined to become the XP-40, prototype for the P-40 Warhawk
75Q: Two fixed undercarriage demonstrators
H75R: The 75J with a different supercharger
75S: Curtiss designation for the XP-42
US Army Designations
Y1P-36: Three pre-production machines, Pratt & Whitney engines and two machine guns in the nose, one 0.30in and one 0.50in
P-36A: Main production version, similar to Y1P-36
P-36B: One aircraft used to test supercharger gearing
P-36C: The final thirty machines, built with two extra 0.30in machine guns in the wings
XP-36D: One aircraft with standard nose armament and four 0.30in wing guns
XP-36E: One aircraft with six 0.30in wing guns
XP-36F: One aircraft with two 23mm Madsen cannon carried under the wings
P-36G: Thirty H75A-8s taken over from Norway
US Service Career
The P-36 served with ten Pursuit Groups and one Composite Group of the Army Air Corps. The 1st, 8th and 20th Pursuit Groups all used it in the United States, but had replaced it with more modern aircraft before December 1941, as had the 18th Pursuit Group on Hawaii. The 16th and 32nd Pursuit Groups both operated the P-36 in the Panama Canal Zone. The 16th replaced in it 1941, but the 32nd may have kept some into 1943 when it was disbanded. The 35th and 36th Pursuit Groups operated the P-36 while they were training up after being formed, but both replaced it before moving overseas - the 35th to the Philippines and the 36th to Puetro Rico.
The P-36 was the standard Air Corps fighter of 1939. It, the A-17 and the B-18 accounted for 700 of the 800 first line aircraft in the corps. Even by 1939 it was obsolescent, with a lower service ceiling, top speed and weaker armament than the Spitfire of Bf 109. Worse, the P-36 was at the peak of its development while both the British and German fighter had plenty of scope for further improvements.
Only two groups were operating the P-36 on 7 December 1941. The 28th Composite Group, in Alaska, was equipped with twelve B-18As and twenty P-36s. The 15th Pursuit Group, on Hawaii, was equipped with a number of P-36s, alongside more modern P-39s and P-40s. All of these modern aircraft had only recently arrived on Hawaii. Thirty-one P-36s with their pilots and crew chiefs had departed for Hawaii on the carrier Enterprise in February 1941, soon followed by the P-40s.
Very few American fighter aircraft were able to get into the air during the Japanese attack on Pearl Harbor. Thirty-five minutes after the initial attack two P-36s and four P-40s were able to take off from Wheeler Field, and at 08.50 another four P-36s of the 46th Pursuit Squadron were able to get into the air. They attacked a Japanese formation near Bellows Field, shooting down two Japanese aircraft for the loss of one P-36. The 47th Pursuit Squadron at Haleiwa airfield was the most successful unit on the day. Their base wasn't subject to the same heavy attacks as Wheeler Field, and between 08.15 and 10.00 a small number of pilots were able to fly repeated sorties, often alternating between the P-36 and P-40. After the attack was over the surviving P-36s took part in the unsuccessful attempts to locate the Japanese fleet. After Pearl Harbor the P-36 rapidly went out of service. By the summer of 1942 VII Fighter Command on Hawaii had 28 P-26s, of which 22 were serviceable, but had five times more P-40s, with 101 serviceable out of a total of 134.
Curtiss Model 75 (First prototype in first configuration)
Engine: Wright SCR-1670-G5
Wing span: 37ft 0in
Length: 28ft 3.5in
Height: 9ft 1in
Empty Weight: 3,760lb
Gross Weight: 4,843lb
Max Speed: 281mph at 10,000ft
Cruising Speed: 250mph
Service Ceiling: 30,000ft
Range: 537 miles
Armament: Two machine guns
Engine: Pratt & Whitney R-1830-13
Wing span: 36ft 3.5in
Length: 28ft 10in
Height: 9ft 0in
Empty Weight: 4,267lb
Gross Weight: 5,414lb
Max Speed: 293mph at 10,000ft
Cruising Speed: 261mph
Service Ceiling: 31,500ft
Range: 790 miles
Armament: One 0.50in and one 0.30in machine gun
Engine: Pratt & Whitney R-1830-13 or 17
Power: 1,050hp at 10,000ft
Wing span: 37ft 4in
Length: 28ft 6in
Empty Weight: 4,567lb
Gross Weight: 5,470lb
Max Speed: 313mph at 10,000ft
Service Ceiling: 33,000ft
Range: 825 miles at 270mph at 10,000ft
Armament: One .50in and one .30in machine guns in nose