The Seversky P-35 was the first American fighter with a retractable landing gear, the first of all-metal construction, and the first with an enclosed cockpit. However, it was produced at a time in which fighter designs were evolving quite rapidly, and rapidly became obsolete. Consequently, its service with the USAAC was rather short.
The Seversky Aircraft Corporation was the brainchild of Alexander Prokofieff de Seversky, who was born in Russia in 1894. de Seversky had been an officer in the Tsar's armed forces during World War I, and emerged from the war as Russia's third leading ace, with 13 kills to his credit. When the Bolshevik Revolution came to Russia in 1917, de Seversky was serving as an air attache in the United States and he decided that it would not be a good idea to return home. de Seversky subsequently became an American citizen and later became a Major in the USAAC reserve.
In 1931, Major de Seversky and a group of investors founded the Seversky Aircraft Corporation of Farmingdale, Long Island. His chief engineer was Alexander Kartveli, another emigre from Russia.
The first product of the new company was the SEV-3, an amphibious all- metal monoplane with a low-mounted cantilever wing. The "3" in the designation stood for the number of crew members it could carry. The plane was built in a hangar rented from the Edo Aircraft Corporation, a well-known manufacturer of floats for airplanes. The twin floats had retractable wheels.
The SEV-3 flew for the first time in June, 1933. Six examples were built for Colombia, where they were used as amphibious reconnaissance aircraft. On September 15, 1935, the original SEV-3 was used to set a world speed record for piston-engined amphibious airplanes of 230.413 mph, which still stands.
A two-seat landplane version with dual controls was derived from the SEV-3, and in 1935 the USAAC ordered 30 examples under the designation BT-8. The BT-8 became the first all-metal low-wing monoplane trainer to enter service with the USAAC, introduced just at the time that the biplane was being phased out of the pursuit and observation categories. It was also the first Army basic trainer specifically built for the purpose rather than being a converted observation or a converted primary trainer. The engine was a 450 hp Pratt & Whitney R-985-ll Wasp Jr. engine, and the maximum speed was 175 mph at sea level.
In 1935, the Seversky company produced a privately-financed experimental fighter known as SEV-2XD, which stood for "Seversky Two-Seat Experimental Demonstrator". The SEV-2XD aircraft was powered by an 850 hp Wright R-1820 radial air-cooled engine driving a three-bladed propeller. The design used a low-mounted elliptical wing. The two cremembers sat in tandem under a transparent cockpit hood, and the rear crewmember was provided with a flexible gun mount for protection against attacks from the rear. The SEV-2XD had a fixed undercarriage enclosed by large wheel pants. The designation was soon changed to SEV-2XP (P for "Pursuit"), when Seversky decided to enter the aircraft in the USAAC's May 1935 competition for a single-seat monoplane to replace the Boeing P-26 currently in service.
The SEV-2XP was completed in the spring of 1935. However, Major de Seversky quickly learned that his two competitors, the Curtiss Model 75 and the Northrop 3A, both had retractable undercarriages. On June 18, 1935, the SEV-2XP was "badly damaged" in an accident while on its way by road to Wright Field for entry into the competition, and the airplane was taken back to the Farmingdale factory for repairs. Some cynics have suggested that this "accident" was contrived by de Seversky as a ruse on his part to buy him and his company enough time to modify the design.
The Seversky company stalled the USAAC competition while they hastily modified the SEV-2XP prototype in the hope of making it more competitive. The two-seater became a one-seater, and a retractable undercarriage was fitted. The undercarriage wheels were partially faired and the wheels remained partially exposed when the legs retracted rearward into fairings mounted underneath the wing. The tailwheel was retractable, and the single-seat cockpit was fully enclosed by a sliding canopy. A new 850 hp Wright R-1820-G5 Cyclone air-cooled radial engine was fitted. The company redesignated the aircraft as SEV-1XP, the "1" for a single seat. Armament was two 0.30-cal machine guns mounted in the upper fuselage, synchronized to fire through the propeller arc.
The newly-revised SEV-1XP finally arrived at Wright Field on August 15, 1935. Needless to say, the Curtiss company was extremely annoyed at being confronted by what was basically a new competitor at this late stage. In the meantime, the USAAC had postponed the flyoff until April of 1936, since one of the other competitors, the Northrop 3A, had crashed into the sea at the end of July during its very first test flight. During early test flights at Wright Field, the SEV-1XP was able to attain only 289 mph at 10,000 feet, rather than the 300 mph actually promised. The delay in the competition gave de Seversky some time to modify his design still further. It was concluded that the troublesome Cyclone engine might be the cause of the poor performance of the SEV-1XP, and this engine was replaced by an 850 hp Pratt & Whitney R-1830-9 Twin Wasp. The re-engined aircraft was redesignated SEV-7. Simultaneously, new vertical tail surfaces were fitted. However, the Twin Wasp engine was found to yield only 738 hp, and the top speed of the new fighter dropped still further, down to 277 mph.
In the meantime, Curtiss had fitted its Model 75 prototype with a new Wright XR-1820-39 radial engine. In addition, the Vought company had bought the 3A design from Northrop and entered a new competitor based on this design under the company designation V-141. Consolidated had also entered the fray, with a single-seat adaptation of its PB-2A two-seat fighter.
After some further modifications to the SEV-7, the designation was changed to AP-1. Although the Seversky fighter never lived up to its promised maximum speed of 300 mph, it was judged by the USAAC as the best of the entries, and on June 16, 1936, Seversky was awarded a contract for 77 examples under the designation P-35. Serial numbers were 36-354/430.
The P-35 was closely reminiscent of the SEV-7, with a cantilever, low-mounted wing. The wing was entirely of metal with the exception of the control surfaces, which were fabric covered. The 850 hp Pratt & Whitney R-1830-9 radial engine was enclosed by a tight cowling. Armament was the American standard of the day, one 0.50-inch and one 0.30-inch machine gun in the upper fuselage deck, synchronized to fire through the propeller arc. The armament of the P-35 was rather light in comparison to that which was becoming standard elsewhere in the world, in particular with the contemporary Hawker Hurricane which carried eight machine guns. Maximum speed of the P-35 at 10,000 feet was 282 mph. An altitude of 15,000 feet could be reached in 6.9 minutes. Service ceiling was 30,600 feet. Empty and loaded weights were 4315 lb and 5599 lb respectively. Maximum range was 1150 miles.
The first production P-35 (36-354) had no wing dihedral and large bulging fairings that completely enclosed the wheels. Testing at Wright Field revealed that the aircraft was extremely unstable and had some rather dangerous flying characteristics. Stability was improved by adding several degrees of dihedral to the wing and replacing the full wheel fairings by partial fairings.
The first delivery of a P-35 to the USAAC was in July 1937. Deliveries of the P-35 to the USAAC were exceedingly slow because of the Seversky company's inexperience with mass production, and it was not until the spring of 1938 that the 17th, 27th, and 94th Squadrons of the First Pursuit Group at Selfridge Field, Michigan actually received their first P-35s.
In the meantime, the USAAC was becoming exceedingly nervous about Seversky's tardiness in meeting production schedules and decided to hedge its bets. On July 30, 1937, the USAAC ordered 210 Curtiss P-36s, a production version of the Curtiss Model 75 which had come in second in the 1936 competition.
The last P-35 of the original order was delivered in August 1938. After flying for a few months with the 1st Pursuit Group, the P-35s were redistributed among squadrons of the 31st, 49th, 50th, 53rd, and 58th Groups, pending the arrival of the P-36 fighters into service.
In the meantime, the original SEV-1XP was rebuilt as a racing aircraft (S-1). The armament was removed, and various aerodynamic refinements were fitted. It took fourth place in the 1937 Bendix race from Burbank, California to Cleveland, Ohio. A sister ship, the S-2, was equipped with a 1000 hp R-1830 engine and won the 1937 Bendix race. The same aircraft was entered in the 1938 Bendix race and came in second place due to engine trouble. The S-2 won the Bendix event again in 1939, at an average speed of 282 mph.
The Seversky company modified a P-35 into the AP-1, a company-owned aircraft used for trail purposes. It had a new tight-fitting couwling and a large pointed spinner to reduce drag. It was tested at Wright Field. The AP-2 featured a flush-retracting gear for greater speed.
The last aircraft on the P-35 contract (36-430) was delivered in 1938 as the XP-41 with a revised wing and a 1200-hp R-1830-19 engine with a turbosupercharger. It made its first flight in March, 1939, shortly before the Seversky company changed its name to Republic Aviation Corporation. A maximum speed of 323 mph at 15,000 feet was attained, but the Army preferred a parallel development, the high-altitude AP-4 which was eventually to emerge as the YP-43, and the XP-41 was not developed any further.
By 1940, it was clear that the rapid advances in military aviation were quickly making the P-35 fighter obsolete. The P-35 was too slow, too lightly-armed, and was lacking in such protections as armor for the pilot or self-sealing fuel tanks. The shotgun engine starter often jammed, the engine tended to leak oil, and the gear retraction mechanism was often found to be faulty. Consequently, the service life of the P-35 with the USAAC was rather brief. By early 1941, most of the Army P-35s had been replaced in front-line service by the Bell P-39 Airacobra or by the Curtiss P-40. As P-35s were removed from service with front-line combat units, they were transferred to training units or were used at ground schools for the training of mechanics. By the time of Pearl Harbor, no P-35s were in active Army combat service.
There is a P-35 on display at the Wright-Patterson Air Force Base Museum in Dayton, Ohio. The plane is serial number 36-404, and it is painted in the markings of the 94th Pursuit Squadron, based as Selfridge Field in Michigan.