The Curtiss P-3 Hawk was a version of the Hawk fighter powered by the Pratt & Whitney Wasp radial engine. Only six were produced and the Army stuck with inline engines, but the navy adopted the radial engine for its Hawks.
The first XP-3 was the final P-1A (25-300). Originally it was to be completed with the Curtiss R-1454 air-cooled radial, but this engine was a failure and so the aircraft was built with a Pratt & Whitney Wasp radial with the designation XP-3A. Tests on the XP-3A began in April 1928. This aircraft later became one of two XP-21s.
In December 1927 the Army ordered five production versions of the XP-3A, as the P-3A. Deliveries began in September 1928 and these aircraft were used for service tests of the new Wasp radial engine in a fighter airframe. They were operated by the 94th Pursuit Squadron.
The first of the five production aircraft later became a second XP-3A and was used in the development of the NACA Cowling. This aircraft, with a tight cowling and large spinner, took part in the 1929 National Air Races. Both XP-3As were late given Wasp Jr engines with the designation XP-21. It came second in the Free-for-All race with an average speed of 186mph. This was the last time the Army took part in a race against civilian aircraft. This aircraft (28-189) went on to become a second XP-21 before finally becoming a P-1F.
The Wasp engine performed better at high altitude than the standard Curtiss D-12 and Conqueror engines. The Navy responded by installing the Wasp engine in their F6C-4 fighters, but the Army persisted with the inline engines, combining them with turbo-superchargers in an attempt to improve their high-altitude performance.
Power: Pratt & Whitney R-1390-3
Span: 31ft 7in
Length: 22ft 11n
Height: 8ft 9in
Empty weight: 2,024lb
Loaded weight: 2,730lb
Max speed: 153mph at sea level, 148mph at 10,000ft
Cruising speed: 137mph
Climb Rate: 1,742ft/ min
Service ceiling: 23,000ft
Range: 342 miles
Armament: Two .3in machine guns