Douglas P3D flying boat
Developed from the Dolphin, in parallel for the USAAC as the B-11 amphibious flying boat bomber, and tendered for the USN as a standard flying boat as the P3D in competition against the PBY.
The YB-11 concept was abandoned by the USAAC, the aircraft was redesignated as the YO-44 and then completed as the YOA-5. No further aircraft were built.
The YP3D-1 was completed as a flying boat with permanent beaching gear, undercarriage too weak to absorb landing and take-off stresses, but allowing the aircraft to be brought onto land without maintenance. The PBY entered production due to cost, and the P3D was rebuilt to become the YP3D-2 with retractable floats, in competition with the PBY-2. Again the PBY-2 entered production, with only the single P3D constructed.