In 1933, the
United States Navy placed orders with both Douglas and
Consolidated Aircraft for single prototypes of patrol flying boats, to replace the
Consolidated P2Y and Martin P3M that equipped the Navy's patrol squadrons. Douglas's design, the P3D, was designed in parallel with the smaller
YB-11 being developed for the
United States Army Air Corps (which was eventually built as the YOA-5), and like the YB-11, was a twin-engined high-winged
monoplane with its engines (the new
Pratt & Whitney R-1830 Twin Wasp
radial engine mounted in nacelles above and ahead of the wing. Unlike the YB-11, it was a pure flying boat rather than an
amphibian, and was therefore fitted with retractable beaching gear to allow it to be moved to and from shore, rather than a full undercarriage allowing operation from land or sea. The Douglas prototype, designated
XP3D-1, first flew on 6 February 1935, and was delivered to
NAS San Diego for testing in March 1935. demonstrated very similar performance, Douglas re-designed the P3D to improve performance in order to win follow-on contracts, and rebuilt the XP3D-1, raising the wing by 27 inches (0.69 m) and mounting the engines on the leading edge of the wing. The fixed wing floats were replaced by retractable floats, and a nose turret was fitted. The rebuilt aircraft, designated
XP3D-2 was re-delivered on 15 May 1935, but production orders again went to Consolidated, for the improved PBY-2. ==Operational history==