As a contender in the 1937 US Navy shipboard single-seat fighter competition, the Seversky-designated NF-1 (Naval Fighter No 1) was derived from the basic P-35. Wssentially a P-35 with a Cyclone instead of P&W R-1830, arrestor hook, bomb racks, and AP-1’s rearward-retracting gear.

The design was flown for the first time on 3 May 1937 piloted by C H Miller, registered NX1254. Powered by a Wright R-1820-22 Cyclone nine-cylinder radial rated at 950hp for take-off and having provision for one 7.62mm and one 12.7mm gun in the forward fuselage, the NF-1 was delivered to Anacostia NAS for evaluation under the US Navy designation XFN-1 on 24 September 1937 on some USN records as A8978. This designation was actually applied for “book-keeping purposes”, no Navy contract being issued.

The NF-1 had initially flown with a vertical windscreen similar to that first fitted to the AP-1, but this had been replaced by a more conventional windscreen prior to delivery to Anacostia. At an early phase in the evaluation the fairings attached to the main oleo legs, which fully enclosed the undercarriage when retracted, were removed.

By consensus, the XFN-1 lacked the low-speed handling characteristics demanded for shipboard operation and the fighter was rejected by the Navy, further development being discontinued.

Engine: Wright R-1820-22 Cyclone, 950hp
Wingspan: 10.97 m / 36 ft 0 in
Wing area: 20.44 sq.m / 220.01 sq ft
Length: 7.44 m / 24 ft 5 in
Height: 2.77 m / 9 ft 1 in
Max take-off weight: 2373 kg / 5232 lb
Empty weight: 1823 kg / 4019 lb
Max. speed: 430 km/h / 267 mph
Stall: 69 mph
Range: 1570 km / 976 miles
Ceiling: 30,700’
seats: 1

A progressive development of the basic SEV-1XP, the AP-2 (Army Pursuit No 2) differed essentially in having a modified centre wing structure incorporating wells for an entirely new flush-housed inward-retracting undercarriage. Together with a shallower cockpit canopy, these refinements were expected to raise maximum speed above the 483km/h mark. The AP-2 NX1250 c/n 39 was powered by a 1,050hp Pratt & Whitney R-1830-9 Twin Wasp engine and armament was proposed to comprise the standard combination of one 7.62mm and one 12.7mm machine gun. It was ascertained that the flush-retracting undercarriage did not result in as much drag reduction as anticipated, but performance was still markedly superior to that of the P-35. Seversky’s bid price was considered too high, however, and the AP-2 was rejected by the USAAC. It had been entered in the September 1937 Bendix Trophy contest as NR1250, but prior to this event suffered an undercarriage failure while landing at Floyd Bennett Field. Much of the airframe was re-used for the AP-7.

Representing an attempt to obtain maximum performance from the basic P-35 design without introducing radical changes, the AP-7 employed much of the airframe of the earlier AP-2 but was powered by a 1,200hp Pratt & Whitney R-1830 Twin Wasp engine. As first completed early in 1938, the AP-7 reverted to the semi-retractable main wheel arrangement of the P-35, and in this form NX1384 c/n 145 was used by the celebrated aviatrix Jacqueline Cochran to capture the 1938 Bendix Trophy, having been used by Maj Alexander P de Seversky two days prior to this event to establish a new US transcontinental record with an elapsed time of 10 hr 3 min 7 sec.

The AP-7 was subsequently fitted with a new wing, with an improved leading-edge profile, and an inward-retracting undercarriage similar to that of the AP-2, as the AP-7A in 1939. It did set a speed record of 322mph piloted by Cochran. It was intended that the modified AP-7 should participate in the 1939 Bendix Trophy contest, but was withdrawn after two aborted take-offs.

It is generally thought the AP-7 was destroyed in a hangar fire in Tampa FL, but one account claims it was sold in a somewhat irregular transaction to Ecuador’s Fuerza Aerea for $40,000 in 1941.

The 1937 AP-9 NX2598 c/n 148 sister ship to the AP-7 was for pursuit trials. It went to the Dominican Republic late in 1940.

AP-7 / AP-7A
Engine: 950hp P&W Twin Wasp
Wingspan: 36’0″
Length: 25’0″
Seats: 1

Preceded by the AP-7, the AP-4 possessed a superficial resemblance to the AP-2 and was intended as a high-altitude interceptor. The first Seversky fighter to feature flush-riveted skinning, the AP-4 was powered by a 1,200hp Pratt & Whitney R-1830-SC2G equipped with a belly-mounted turbo-supercharger. As a company- funded development, the AP-4 was intended to participate in a USAAC competition scheduled for 25 January 1939 and was expected to demonstrate the superior medium- and high-altitude performance obtainable with a turbo-supercharged R-1830. The same engine, fitted with a mechanical supercharger, had been specified by the USAAC for the XP-41.

First flying on 22 December 1938, piloted by Frank Sinclair, the AP-4 NX2597 c/n 144 was evaluated at Wright Field during February- March 1939, demonstrating exceptional climb and altitude performance.

Early 1939, it was fitted with a close-fitting, high-inlet-velocity engine cowling matched with an oversize propeller spinner as a continuation of a drag reduction programme supervised by the NACA and initiated earlier with the AP-1. The AP-4 was subsequently fitted with a modified engine cowling, without the spinner, but, on 22 March 1939, caught fire in the air, the pilot bailing out. On 12 May 1939, a contract was awarded for 13 service evaluation models under the designation YP-43.

Engine: P&W turbocharged R-1830-SC Twin Wasp, 1100hp
Wingspan: 10.97 m / 36 ft 0 in
Length: 8.23 m / 27 ft 0 in
Height: 3.81 m / 13 ft 6 in
Wing area: 20.44 sq.m / 220.01 sq ft
Max take-off weight: 3075 kg / 6779 lb
Empty weight: 2462 kg / 5428 lb
Max. speed: 534 km/h / 332 mph
Stall: 78 mph
Range: 1255 km / 780 miles

When, in 1936, the USAAC Materiel Division placed an order for the SEV-1XP as the P-35, it had stipulated that the 77th and last series aircraft be fitted with a more powerful supercharged engine. The chosen engine was the Pratt & Whitney R-1830-19 of 1,200hp, fitted with an integral medium-altitude two-stage mechanical supercharger.

A contractual modification enabled Seversky to complete the airframe to a standard similar to that of the private-venture AP-4. The AP-9 was, in fact, used for competitive evaluation at Dayton in lieu of the XP-41 until the latter became available. Power plant apart, the aircraft was in virtually all respects similar to the AP-4.

The XP-41 36-430 was delivered to Wright Field for USAAC evaluation in February 1939, but the Air Corps preferred the turbo-supercharged AP-4 and further development of the XP-41 was discontinued, although trials continued at Langley. This was the last of the Kartveli-designed fighters to bear the Seversky appellation, as the company thereafter became the Republic Aviation Corporation.

Engine: P&W R-1830, 1200hp
Wingspan: 10.97 m / 36 ft 0 in
Wing area: 20.44 sq.m / 220.01 sq ft
Length: 8.23 m / 27 ft 0 in
Height: 3.78 m / 12 ft 5 in
Max take-off weight: 3175 kg / 7000 lb
Empty weight: 2445 kg / 5390 lb
Useful load: 1210 lb
Max. speed: 520 km/h / 323 mph
Cruise speed: 290 mph
Ceiling: 7000 m / 22950 ft
Range: 789 km / 490 miles
Armament: 1 x 7.62mm + 1 x 12.7mm machine-guns

The 1937 Seversky AP-1 was rejected P-35 36-354 refitted with a 750hp P&W R-1830 engine. First flown on 4 May 1937, piloted by A de Seversky, only the one was built, X/NR1390 c/n 44, for Wright Field and NACA testing. It was used as a company demonstrator until it was destroyed in a 1938 hangar fire.

Engine: 750hp P&W R-1830
Wingspan: 36’0″
Length: 25’4″
Top speed: 277 mph

The 1938 Seversky EP1-68 NX2587 c/n 147 was a European demonstrator, but sold to the Ecuador AF in 1941.

Engine: 1200hp P&W P-1830-S1C Wasp
Wingspan: 36’0″
Length: 26’10”
Speed: 290 mph
Seats: 1
Undercarriage: retractable

The Alexander de Seversky SEV-S2 was a modified civil competition version of the Army P-35 for the Nationals.

Registered NR70Y c/n 43 and piloted by Frank Fuller Jr, it raced in the 1937 and 1939 Bendix Trophy, and reached second place in the 1938 Bendix.

SEV-S2 1937
Engine: 950hp P&W R-1830 Twin Wasp SC
Seats: 1

The 1936 Seversky SEV-X-BT NX189M c/n 6 was built for military evaluation as a basic trainer, but lost out to North American BT-9.

It was dismantled for parts, much of which went into the 2PA-L. The registration was possibly transferred to 2PA.

SEV-X-BT
Engine: 550hp P&W R-1340-S3H1
Wingspan: 36’0″
Length: 20’5″
Speed: 180 mph
Seats: 2