The DF was an all-metal high-wing monoplane with fabric-covered control surf aces. Smooth sheet metal skin was used except on the forward two-thirds of the wing which had corrugated skin. The hull was of the two-step type and the single-step stabilizing floats were hydraulically-retracted inward and partially recessed into the underside of the wing.
Power was supplied by two 1,000 hp Wright SGR-1820G-2 nine-cylinder driving three-blade constant-speed propellers. Accommodation was for a maximum of 32 passengers in four 8-seat compartments and for night service the normal seating could be replaced by 16 berths. The crew of four consisted of pilot, co-pilot, navigator and stewardess. The aircraft was equipped with galleys, two lavatories, and an aft cargo compartment.
Completed in September 1936, the first DF was successfully tested, however, as Pan American was not interested in operating a twin-engined flying boat on relatively long overwater flights, Douglas found itself without a domestic customer for the prototype and the three additional DFs it had under construction. Fortunately, the company obtained government authorization to sell them to any interested foreign customer.
Two of the Douglas flying boats, which had been completed to Specification DF-151 standards, were shipped to Japan in 1936-37. Officially, as J-ANES and J-ANET, they were for Dai Nippon Koku KK (Greater Japan Air Lines). In fact, they were procured for evaluation by the Japanese Navy and designated HXD-1 and HXD-2, Navy Experimental Type D flying boat.
One of the two aircraft was quickly dismantled by Kawanishi to obtain engineering data later used in the design of its four-engined H8K flying boat. The other aircraft was operated on survey flights, and on 10 August, 1938, during one of these, it crashed at sea.
The last two aircraft, built as DF-195s, were purchased by the Soviet Government and in 1937 were flown to the USSR via Alaska and across the Bering Sea. At least one, registered SSSR-N-205, was operated by Aeroflot on the Leningrad-Sevastopol route until about 1940.
Span: 95 ft 0 in (28.96 m)
Length: 69 ft 10.56 in (21.30 m)
Height: 24 ft 6.25 in (7.47 m)
Wing area: 1,295 sq.ft (120.31 sq.m)
Weight empty: 17,315 lb (7,854 kg)
Max T/O weight: 28,500 lb (12,927 kg)
Max speed: 178 mph (286 kmh) at 6,800 ft (2,075 m)
Cruise speed: 160 mph (257 kmh)
Service ceiling: 9,842 ft (3,000 m)
Initial climb: 800 ft (243 m)/min
Range (fully loaded): 1,500 mls (2,415 km)