Curtiss 75 Hawk

Curtiss 75 Hawk

By Joe Baugher

Model 75A was the company designation for a Curtiss-owned demonstrator [NX22028] used to carry out several company-originated experiments. First it was fitted with an external mechanical supercharger mounted underneath its P&W R-1830 engine and briefly designated Model 75J.

    Then it was experimentally fitted with a turbo-supercharged R-1830-SC2-G. 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. Company designation for the modification was Model 75R. Empty and normal loaded weights went up to 5074# and 6163#. During trials in Jan 1939, it attained a maximum speed of 330 mph at 15,000'. However, poor reliability and complexity of the supercharger led the USAAC to decide not to proceed with that variant of the P-36, choosing instead to purchase the supercharged Seversky (Republic) XP-41.

    After trials at Wright Field, the aircraft was returned to the Curtiss plant in Buffalo, where it was fitted with a Wright R-1820 to resume its role as a demonstrator.


Considerable interest in the Hawk had been aroused in Britain as a result of a test flight carried out with an Armee de l'Air Hawk by an RAF pilot in France. The Hawk 75A possessed remarkably good controls and the ailerons were fairly light at high speeds in contrast with the early Spitfire which had ailerons which were almost immobile at speeds over 300 mph.

    At the end of 1939, the Royal Aircraft Establishment (RAE) arranged for a loan of a Curtiss Hawk from France (the 88th production Hawk 75A-2) for comparative trials against a Spitfire I [K9944]. In many respects, the Hawk turned out to be superior to the Spitfire. RAE found that the Hawk did indeed have exceptional handling characteristics and beautifully harmonized controls. In a diving attack at 400 mph, the Hawk was far superior to the Spitfire I owing to its lighter ailerons. In a dogfight at 250 mph, the Hawk was again superior, because its elevator control was not over-sensitive and all-round view was better.

    However, the Spitfire could break off combat at will because of its much higher speed. When the Spitfire dived on the Hawk, the Curtiss could avoid its opponent by banking and turning rapidly. The Spitfire could not follow the Hawk around and would overshoot the target. The Hawk 75A displayed appreciably superior take-off and climb characteristics. The swing on takeoff was smaller and more easily corrected than on the Spitfire, and during the climb the Hawk's controls were more effective, but it tended to be rather slow in picking up speed in a dive.

    Based on these trials, the British government briefly toyed with the idea of ordering the Hawk for the RAF. For whatever reason, these plans were never carried out. However, the fall of France in June 1940 caused quite a few Hawks to fall into British hands.

    Hawk 75As which had not yet been delivered to France before the surrender (most of them A-4s), plus those whose pilots had flown them to England to escape the German occupation were taken over by the RAF and given the name Mohawk. The total number of Mohawks impressed by the RAF was 229 planes. Most of them were former French machines, but a few former Persian Hawks and even some Indian-built machines were included in the Mohawk total, as well.

    There were four RAF sub-variants—Mohawk I, II, III, and IV. Former French Hawk 75A-1s were named Mohawk I by RAF, with Hawk 75A-2s named Mohawk II. There was a total of 29 of these planes. Yet it is difficult to track which planes were A-1s and which were A-2s, since Mohawk I and Mohawk II aircraft were intermixed with each other and with Mohawk IVs in the RAF s/n blocks [AX880/898, BK876/879, and BL220/223].

    More than 20 former French Hawk 75A-3s were taken over by Britain as Mohawk IIIs. RAF s/ns for these were [BK569/588], but some A-3s were mixed with Mohawk IVs in serial block [AR630/694].

    The name Mohawk IV was assigned to the remainder of the French Hawk 75A-4 order which was taken over by the RAF. The exact number of Mohawk IVs diverted to Britain cannot be determined from RAF serial numbers alone, since some blocks were applied to both IIIs and IVs without distinction. The total number of Mohawks appearing as IVs total 190, only six less than the total of Hawk 75A-4s built.

    However, some 75As other than A-4s became Mohawk IVs, including the 10 A-9s originally intended for Persia and at least six of the former Chinese A-5s assembled in India. Mohawk IV RAF s/ns of record were [AR630/694, BB918/937, BB974/979, BJ434/453, BJ531/550, BJ574/588, BK876/879, BL220/223, BS730/738, BS744/747, BS784/798, BT470/472, LA157/158, LA163/165].

    Mohawks taken on strength by the RAF were refitted with British equipment, including .303 Browning machine guns. French throttles were replaced by throttles which operated in the "British fashion"—pushed forward to increase power. RAF decided that its Mohawks were not suitable for the European theater and sent 72 of them to the South African Air Force, where they were flown by the 3rd, 4th, 5th, 6th and 7th Squadrons which operated in East Africa, while others were flown by the 5th and 155th RAF squadrons in India. At one time, eight Mohawks provided the sole fighter defense of Northeast India, and the fighter remained operational on the Burma front until finally replaced by more modern types in Dec 1943. Twelve Mohawks were sent to Portugal.

Hawk 75A-5

Hawk 75A-5 was Curtiss' designation for a Cyclone-powered model which was to be assembled in China by the Central Aircraft Mfg Co (CAMCO). At least one complete airplane and some kits of unassembled parts were delivered to China. After assembling some aircraft in China, CAMCO was reorganized as Hindustan Aircraft Ltd in Bangalore, India. In Apr 1941 the Indian government placed a contract with Hindustan for the construction of 48 Cyclone-powered 75As, together with necessary spares.

    Hindustan acquired a manufacturing license from Curtiss, and the first Indian-built machine flew on July 31, 1942. However, shortly after that flight, a change in policy resulted in the decision to abandon the construction of complete aircraft in India. After four more planes were constructed, the Hindustan program was terminated, and the Indian-built machines were absorbed into the RAF as Mohawk IVs.

Hawk 75A-6/75A-8

In the autumn of 1939, the Norwegian government ordered 12 Hawk 75A-6s with 1200hp P&W R-1830-S1C3G Twin Wasps and four-gun armament. This was later supplemented with an order for 12 more. Deliveries began in Feb 1940, but only a few A-6s actually got there before Norway was overrun by the Germans, who captured most of them—some still in their shipping cases—and sold 8 of them to Finland.

    75A-6s for Finland were supplemented by 36 partially-completed Hawk 75As that had been seized by German forces from France at the time of its surrender and assembled in Germany. Those participated in the war on the Axis side when Finland entered the war against the Soviet Union on June 25, 1941. They gave a good account of themselves, and some Hawks remained in service in Finland until 1948.

    Norway ordered an additional 36 75A-8s with 1200hp Wright R-1820-G205A Cyclones just before the German occupation. The German occupation caused the planes to be impounded by the US government before delivery, and 6 were delivered to Free Norwegian forces training in Canada in Feb 1941. The remaining 30 were requisitioned by the US Army as P-36G. Armament was four 0.30 and two 0.50 machine guns.

Hawk 75A-7

Twenty Hawk 75A-7s with Cyclones were ordered by the Netherlands, but the German occupation of Holland caused all of them to be diverted to the Netherlands East Indies starting in May 1940. They served with the 1st Squadron of the Royal Netherlands East Indies Army Air Corps, where they were caught up in the Japanese advance from Dec 8, 1941. Outnumbered and outperformed by the Japanese Zero fighters, by Feb 1, 1942, all were destroyed by the enemy.

Hawk 75A-9

The government of Persia (now Iran) ordered 10 Hawk 75A-9s with Wright R-1820-G205A, which arrived shortly before that country was occupied by British and Russian forces on Aug 25, 1941. The Hawks were discovered there still in their shipping crates and taken over by the British, who transferred them to India as Mohawk IVs for the 5th Squadron of the RAF

Hawk 75H

Early in 1937, Curtiss began the development of a "simplified" version of Y1P-36 intended specifically for export. Curtiss was aware that some potential customers whose air arms operated under relatively primitive conditions would look askance at a sophisticated feature such as a retractable undercarriage that promised to afford difficult maintenance problems. The "simplified Hawk" project was given the company designation of Model 75H.

    Construction of the 75H was similar to Y1P-36, but a lower-powered engine was provided and a fixed, single-strut undercarriage with streamlined fairings was fitted. These modifications were first applied to a demonstrator aircraft which was refitted with an 875hp Wright Cyclone GR-1820-GE. The plane, [NR1276], was publicized in Curtiss sales brochures as Hawk 75, with emphasis placed on ease of maintenance, rough field performance, and amenability of the aircraft to accommodate different engines and different types of armament to suit a customer's requirements. It was sold to the Chinese government, who presented it to General Claire Chennault for his own personal use.

    A second and more definitive demonstrator aircraft was built which differed from its predecessor in some respects, including the adoption of the more deeply-scalloped decking immediately aft of the cockpit and revised windshield arch and canopy framing. Armament was supplemented by an additional pair of .30 machine guns in the wings, firing outside the propeller arc. Provision was made for the attachment of underwing bomb racks capable of carrying ten 30# or six 50# bombs, plus a centerline rack for a single 500# bomb. This aircraft was civil registered as [NR1277] and was sold to Argentina.

Hawk 75M

The first overseas customer for Hawk 75 was the Chinese Nationalist government in an order of of 112 Hawk 75s with fixed undercarriage, 875hp GR-1820-G3 Cyclone engine, and two .30 guns in the nose and two in the wings. These planes were to be built by Curtiss and delivered as major components to the Central Aircraft Mfg Co (CAMCO) at Loi-Wing, where they would be assembled and delivered to Chinese units. They were retroactively assigned the designation Hawk 75M by Curtiss. Aside from the additional wing guns and some minor revisions to the undercarriage fairings, they were identical to the second "simplified Hawk" demonstrator.

    It is uncertain just how many Hawk 75Ms actually ended up in Chinese service. Only 30 Hawk 75Ms are accounted for in Curtiss records, with deliveries beginning in May of 1938. Tooling and kits for an unspecified number were delivered to CAMCO for assembly, and an unspecified number were built there. Three full squadrons of 75Ms are known to have been operational, but achieved few successes against the Japanese, largely owing to poor serviceability and inadequate training of both pilots and ground crews.

Hawk 75N

The government of Siam (Thailand) also exhibited interest in the Hawk 75 and ordered somewhere between 12 and 25 examples (the exact number is uncertain and depends on which source you pick). These were given the designation Hawk 75N by Curtiss, and were generally similar to the Chinese 75Ms except for some minor revisions to the main wheel fairings and some differences in the armament. Sources also differ in the armament fitted—one claims that armament was two nose guns (one .30 and one .50) and four .30 wing guns; another claims there were two 23mm Danish Madsen cannon housed in detachable underwing fairings.

    Twelve 75Ns were delivered to Siam starting in Nov 1938. They were involved in the Thai invasion of Indo-China in Jan 1941, the first recorded combat taking place on Jan 11 when four 75Ns escorted nine Martin 139s in an attack on the French airfield at Nakorn Wat. The formation was intercepted by four French Morane-Saulnier M.S.406s. In the resulting air battle, the Thai Hawks claimed two Morane fighters (although the claim was later refuted by the French). On Dec 7, 1941, Thai Hawks were in action again, this time against invading Japanese forces. In the brief battle, a third of the serviceable Hawks were destroyed. Those not destroyed were seized by the Japanese. One example is now in the Royal Thai Air Museum in Bangkok.

Hawk 75O

After purchasing the 75H demonstrator [NR1277] c/n 12328, the Argentine government ordered 29 production examples of the fixed-gear Hawk 75 with 875hp Cyclone. Designated Hawk 75O by the Curtiss, these planes had a similar undercarriage to the Thai Hawk 75N and featured a redesigned engine exhaust system with a semi-circle of electrically-operated gills at the rear of the cowling. Armament was four 7.62mm Madsen machine guns. The first Hawk 75O was completed by Curtiss in late Nov 1938. The planes were serialed C-601 through C-630.

   At the same time, Argentina acquired a license to manufacture the 75O at the Fabrica Militar de Aviones. The first FMA-built Hawk was delivered on Sep 16, 1940. A total of 20 was built, with serials being C-631 to C-650. Some of the Hawks remained in service for over a decade, the last ones operating from El Plumerillo in western Argentina until 1953, when they were transferred to training units until being withdrawn.

Model 75Q

Model 75Q was the designation assigned to two additional fixed-gear demonstrators with R-1820 engines. One was converted to retractable undercarriage configuration and was presented to Mme Chiang Kai-Shek. She in turn gave it to Genl Claire Chennault, who was then reorganizing the Chinese Air Force. The other was flown as a demonstrator in China by American pilots, but crashed on takeoff on May 5, 1939.

-- Air Enthusiast, Volume 1, William Green et al (Doubleday 1971)
-- Curtiss Aircraft, 1907-1947, Peter M Bowers (Naval Institute Press 1979)
-- The Curtiss Hawk 75, Aircraft in Profile #80 (Profile Publications 1966)
-- War Planes of the Second World War, Fighters, Volume 4, William Green (Doubleday 1961)