Curtiss P-36 Hawk
The Curtiss P-36 Hawk, also known as the Curtiss Hawk Model 75, is an American-designed and built fighter aircraft of the 1930s and 40s. A contemporary of the Hawker Hurricane and Messerschmitt Bf 109, it was one of the first of a new generation of combat aircraft—a sleek monoplane design with a retractable undercarriage making extensive use of metal in its construction.
Perhaps best known as the predecessor of the Curtiss P-40 Warhawk, the P-36 saw little combat with the United States Army Air Forces during World War II. It was the fighter used most extensively and successfully by the French Air Force during the Battle of France. The P-36 was also ordered by the governments of the Netherlands and Norway but did not arrive in time to see action before both were occupied by Nazi Germany. The type was also manufactured under license in China, for the Republic of China Air Force, as well as in British India, for the Royal Air Force and Royal Indian Air Force.
Axis and co-belligerent air forces also made significant use of captured P-36s. Following the fall of France and Norway in 1940, several dozen P-36s were seized by Germany and transferred to Finland; these aircraft saw extensive action with the Finnish Air Force against the Soviet Air Forces. The P-36 was also used by Vichy French air forces in several minor conflicts; in one of these, the Franco-Thai War of 1940–41, P-36s were used by both sides.
From mid-1940, some P-36s en route for France and the Netherlands were diverted to Allied air forces in other parts of the world. The Hawks ordered by the Netherlands were diverted to the Dutch East Indies and later saw action against Japanese forces. French orders were taken up by British Commonwealth air forces, and saw combat with the South African Air Force against Italian forces in East Africa, and with the RAF over Burma. Within the Commonwealth, the type was usually referred to as the Curtiss Mohawk.
With around 1,000 aircraft built by Curtiss, the P-36 was a commercial success for the company. It also became the basis of the P-40 and two unsuccessful prototypes: the P-37 and the XP-42.
Design and development
The Curtiss Model 75 was a private venture by the company, designed by former Northrop Aircraft Company engineer Don R. Berlin. The first prototype, constructed in 1934, featured all-metal construction with fabric-covered control surfaces, a Wright XR-1670-5 radial engine developing, and typical United States Army Air Corps armament of one and one machine gun firing through the propeller arc. Also typical of the time was the total absence of cockpit armor or self-sealing fuel tanks. The distinctive landing gear, which rotated 90° to fold the main wheels flat into the thin trailing portion of the wing, resting atop the lower ends of the maingear struts when retracted, was a Boeing-patented design for which Curtiss had to pay royalties.The prototype first flew on 6 May 1935, reaching at during early test flights. On 27 May 1935, the prototype was flown to Wright Field, Ohio, to compete in the USAAC fly-off for a new single-seat fighter, but the contest was delayed because the Seversky entry crashed on its way there. Curtiss took advantage of the delay to replace the unreliable engine with a Wright XR-1820-39 Cyclone producing and to rework the fuselage, adding the distinctive scalloped rear windows to improve visibility. The new prototype was designated Model 75B with the R-1670 version retroactively designated Model 75D. The fly-off finally took place in April 1936. Unfortunately, the new engine failed to deliver its rated power and the aircraft only reached.
Although the competing Seversky P-35 also underperformed and was more expensive, it was still declared the winner and awarded a contract for 77 aircraft. However, on 16 June 1936, Curtiss received an order from USAAC for three prototypes designated Y1P-36. The USAAC was concerned about political turmoil in Europe, and about Seversky's ability to deliver P-35s in a timely manner, and therefore wanted a backup fighter. The Y1P-36 was powered by a 900 hp Pratt & Whitney R-1830-13 Twin Wasp engine, and the scalloped rear canopy was further enlarged. The new aircraft performed so well that it won the 1937 USAAC competition with an order for 210 P-36A fighters.
The aircraft's extremely low wing loading of just 23.9 lb/ft2 gave it outstanding turning performance, and its high power-to-weight ratio of 0.186 hp/lb gave superb climbing performance for the time. The single speed supercharger was a serious handicap at high altitudes. Compared to the later Allison-engined P-40, the P-36 shared the P-40's traits of excellent high-speed handling, roll rate that improved at high speed, and relatively light controls at high speed. However, it was underpowered, affecting its acceleration and top speed, and it did not accelerate in a dive as well as the P-40.
Operational history
Argentina
Argentina bought a number of the simplified, fixed landing gear Hawk 75Os, and purchased a manufacturing license for the type; 30 were built and delivered by Curtiss, and 20 produced locally. These aircraft used the same engine, Wright Cyclone R-1820-G5 as the Martin 139WAA's and Northrop 8A-2s used by the Argentine Army Aviation at the time. Usually armed with one Madsen machine gun heavily modified for aircraft use and three Madsen light machine guns, there was provision for up to 10 bombs on underwing pylons. The last Argentinian Hawks remained in service until November 1954.Brazil
In March 1942, 10 USAAC P-36As were transferred to Brazil.British Commonwealth
The Royal Air Force also displayed interest in the aircraft. Comparison of a borrowed French Hawk 75A-2 with a Supermarine Spitfire Mk I revealed that the Hawk had several advantages over the early variant of the iconic British fighter. The Hawk was found to have lighter controls than the Spitfire at speeds over, especially in diving attacks, and was easier to maneuver in a dogfight. The Hawk also had better all-around visibilityand was easier to control on takeoff and landing. Not surprisingly, the Spitfire's superior acceleration and top speed ultimately gave it the advantage of being able to engage and leave combat at will.
Although the British decided not to purchase the aircraft, they soon came into possession of 229 Hawks by way of shipments diverted from occupied France and aircraft flown by escaping French pilots. The aircraft received the designations Mohawk I through IV, mirroring French Hawk 75A-1 through A-4, and were fitted with 0.303-cal. machine guns and conventional throttles.
Although the Hawk was considered obsolete, a number saw service with the RAF and Royal Indian Air Force in India and Burma. In April 1941, the government of British India ordered 48 Cyclone-powered Mohawk IVz for the RIAF, to be built by Hindustan Aircraft. The first such aircraft completed was test flown on 31 July 1942. Only four additional aircraft were completed before the project was abandoned. However, Chinese license production of the Hawk 75A-5 was moved to India, and these aircraft were also absorbed into the RAF/RIAF as Mohawk IVs. They were supplemented by 10 Hawk 75A-9s that were captured in Iran, during the Anglo-Soviet invasion of Iran of August 1941. A further 74 Mohawk IVs that had originally been ordered by France were shipped to India from the United Kingdom. The only RAF units to see combat in Mohawks were No. 5 Squadron RAF and No. 155 Squadron RAF, using the type mainly for bomber escort and ground attack. The type was retired by the RAF/RIAF in 1944.
The South African Air Force received 72 Mohawks. Its first Mohawks were delivered to East Africa in mid-1941, where they were used by 3 Squadron SAAF to support operations in the East African Campaign, taking part in the Battle of Gondar which ended the campaign, and helping to patrol the border with Vichy French held Djibouti. These Mohawks were then sent to South Africa, where, supplemented by fresh deliveries, they were used for training and for home defense.
China
The prototype of the Hawk 75H—a simplified version with fixed landing gear, like the 75O—was eventually sold to the Chinese Nationalist government who presented it to Claire L. Chennault for personal use. China also received two similar demonstrators, the Hawk 75Q. They also used a number of simplified Hawk 75Ms against the Japanese. On 11 January 1939, five Hawk 75Ms of the veteran CAF 25th Fighter Squadron led by commander Liu Yijun were flown to the new wartime capital of Chongqing in preparations for defense duties there; Liu Yijun and his four specially-trained Hawk 75 pilots all died in the crash of transport aircraft in the return flight. These Hawk 75Ms were intended for the newly established 16th and 18th Fighter Squadrons that were previously light attack-bomber squadrons, but did not supersede the increasingly obsolescent Polikarpov I-15 and I-16 that formed the backbone of most of China's fighter squadrons from 1938 to 1941. The Hawk 75A-5 was built under license in China, but production was later moved to India, and these aircraft were absorbed into the RAF as the Mohawk IV.Finland
Hawk 75s captured by German forces in Norway and France were on-sold to Finland. Curtiss had sold 13 aircraft to Norway, and 31 more were captured around the time of the fall of France. These were sold to Finland in October 1940. In total, 44 captured aircraft of five subtypes were transferred to Finland, in three tranches, between 23 June 1941 and 5 January 1944. The aircraft were given serial codes CU-501 to CU-507 and CU-551 to CU-587.In Finnish service, the Hawk was well liked, affectionately called Sussu. The Finnish Air Force enjoyed success with the type, credited with kills by 58 pilots, between 16 July 1941 and 27 July 1944, for the loss of 15 of their own. Finnish Hawk pilots included the type's highest-scoring ace, Altto Kalevi "Kale" Tervo, with between and victories in the type; another ace, Kyösti "Kössi" Karhila, scored or of his victories in the Hawk.
The Finnish Hawks were initially armed with either four or six 7.5mm machine guns. While sufficient during the early phase of the Continuation War, the increasing speeds and armor of Soviet aircraft soon showed this armament was not powerful enough. From 1942, the State Aircraft Factory replaced the fuselage machine guns with either one or two Colt or Browning FN machine guns and installed two or four Browning machine guns in each wing. The 12.7mm Berezin UB or LKk/42 heavy machine guns were also used. The installation of heavier armament did not change the very good flying characteristics of the fighter, and the armament was much more effective against Soviet aircraft. The Finnish Hawks were also equipped with Revi 3D or C/12D gunsight.
Surviving Finnish aircraft remained in service with the FAF aviation units HLeLv 13, HLeLv 11 and LeSK until 30 August 1948, when the last operational Finnish Hawks were put into storage. In 1953, the stored aircraft were scrapped.