The Avro Type 501, and Type 503 were a family of early British military seaplanes.
They were a development of the Avro 500 design and were originally conceived of as amphibious, the prototype being fitted with a single large main float under the fuselage, and two outrigger floats under the wings.
Tests were conducted on Windermere in January 1913.
It was later converted to a twin-float configuration and bought by the British Admiralty.
It now, however, proved too heavy and was converted again, this time to a landplane.
An improved version, designated the 503 was demonstrated to the Inspector of Naval Aircraft, who placed an order for three machines.
The prototype itself was demonstrated for the Imperial German Navy in its seaplane trials in June 1913 and was purchased by the government of the German Empire for evaluation purposes.
Gotha purchased a license from Avro and produced the type as the WD.1.
Unlicensed copies were also built by Albatros, AGO, Friedrichshafen.
Some WD.1s were provided to the Ottoman Empire following their withdrawal from German navy service.
33 ft 0 in (10.06 m)
47 ft 6 in (14.48 m)
12 ft 6 in (3.81 m)
478 sq ft (44.4 m2)
1,740 lb (789 kg)
2,700 lb (1,225 kg)
1 × Gnome Omega Omega 14-cyl two row air cooled rotary piston engine,