In the early 1930s, the Northrop Corporation had produced the Gamma 2C, a company-financed prototype for a two-seat attack aircraft. The Gamma 2C was based on the Gamma 2A and 2B research aircraft. It retained the wings and trousered undercarriage of the previous two Gamma aircraft, but differed from them in having a new fuselage with a new two-seat enclosed cockpit. The cockpit was moved much further forward, with the pilot now sitting slightly behind the wing leading edge.
The Gamma 2C was powered by a 735 hp Wright SR-1820-F2 nine-cylinder air-cooled radial driving a two-bladed propeller. The Gamma 2C was armed with four wing-mounted 0.30-inch machine guns and one flexible 0.30-inch machine gun firing either upward from the rear cockpit or downward through a ventral hatch underneath the fuselage. It was able to carry up to 1100 pounds of bombs externally between its trousered main undercarriage units.
The Army purchased the Gamma 2C under the designation YA-13 on June 28, 1934. The serial number 34-27 was applied.
Flight tests of the YA-13 indicated that the installation of an engine of greater power would result in substantially increased performance. In addition, the large diameter of the Wright SR-1820 radial engine of the YA-13 obscured the pilot's forward view. In order to improve the performance and the pilot's forward visibility, the YA-13 aircraft was returned to Northrop in January of 1935 to be re-engined with the smaller diameter but more powerful 950 hp Pratt & Whitney R-1830-7 Twin Wasp fourteen-cylinder air-cooled radial. This engine change resulted in the YA-13 being redesignated YA-16.
The XA-16 flew for the first time in March of 1935. Flight tests indicated that the XA-16 was now over-powered, and that if the aircraft ever went into production it should either have a smaller engine or else have larger tail surfaces. The Gamma 2F, another private venture project of Northrop, already featured a smaller engine and this version was ordered into production as the A-17, so no further work was carried out on the XA-16.
The XA-16 was later fitted with a 950 hp R-1830-9 engine. It ended its life at an aircraft mechanics' school at Roosevelt Field.
One Pratt & Whitney R-1830-7 Twin Wasp fourteen-cylinder air-cooled
radial, rated at 950 hp for takeoff and 850 hp at 8000 feet.
Performance: Maximum speed 212 mph.
Weights: 6750 pounds maximum.
Dimensions: Wing span 48 feet 0 inches, length 29 feet 8 inches, wing
area 363 square feet.
Armament: Four wing-mounted 0.30-inch machine guns and one flexible
0.30-inch machine gun firing either upward from the rear cockpit or
downward through a ventral hatch. Up to 1100 pounds of bombs could be
carried on external under-fuselage racks.