04/21/2025. Remarks by Johan Visschedijk: "The Curtiss P-3 Hawk was another variant of the basic Curtiss P-1 Hawk airframe. The P-3 series replaced the in-line V-engine of the P-1 and P-2 with a radial engine, however, the P-3 series contained only six aircraft.

XP-3. This designation was assigned to the last P-1A (26-300), which was to be fitted with the new 390 hp Curtiss R-1454 air-cooled radial engine. This proved unsatisfactory before installation in the XP-3 so the designation was cancelled.

XP-3A No.1 (Model 34N). The P-1A that was to have become the XP-3 was completed in October 1927 with the new 410 hp Pratt & Whitney R-1340-1 Wasp nine-cylinder air-cooled radial engine under the designation XP-3A (26-300). This aircraft was originally delivered to the Army uncowled, but was used by the Army at McCook Field to test some early NACA cowling designs for radial engines, it was assigned Project Number "P-451". A later engine changed the designation to XP-21 No.1.

P-3A On December 27, 1927, the Army ordered five Service test versions of the first XP-3A (28-189 to 28-193). These were powered by the 450 hp Pratt and Whitney R-1340-3 engine, deliveries began in October 1928.

XP-3A No.2. This was not a prototype, but the first production P-3A (28-189) which was used for test work for the development of a tight NACA cowling with fuselage faired to match the cowl, and was fitted with a large spinner. It was placed second in the 1929 National Air Race Free-for-All at 186.84 mph (300.69 kmh), when the Army raced against civilians for the last time. Later it was converted to XP-21 No.2, when it was fitted with a 300 hp Pratt and Whitney R-985-1 Wasp Junior engine, then it was brought up to standards of P-1F following a change to a 435 hp Curtiss D-12 (V-1150-3) twelve-cylinder, liquid-cooled V-engine.

The remaining four P-3As were assigned to the 57th Service Squadron at Selfridge Field, Michigan, three were written off at Selfridge: 28-190 on June 3, 1931, 28-192 and 28-193 on December 11, 1928. 28-191 was written off at West Point, New York, on August 15, 1930."