At the end of 1917, a derivative of the HD.1 intended for use by France's Aviation maritime as a single-seat fighter float-plane was tested as the HD.2. Possessing an essentially similar airframe to that of the HD.1, the HD.2 was powered by a 130 hp Clerget 9B rotary engine and carried an armament of twin synchronised Vickers machine guns. Two prototypes were tested with float undercarriages of differing lengths, and several HD.2s with wheel undercarriages were delivered to the Aviation maritime at Dunkirk for trials purposes, including trial operations from a 40-ft (12-m) platform mounted above a turret of the battleship Paris in the harbour at Toulon flown by Lieutenant Georges Guierre in October 1918. Later, in August and September 1918, similar trials were conducted at Saint-Raphael with one of the HD.2 prototypes converted to landplane form and re-engined with a 120 hp Le Rhone. Production examples, designated HD.2C, were fitted with 130-hp Clerget 9B engines, longer main floats, and a completely revised elliptical fin and rudder assembly. Armament comprised twin 0.303-in (7.7-mm) Vickers guns. Some HD.2Cs were in service with the French navy's Centre Maritime at Dunkerque before the end of the First World War.
The US purchased 26 HD.2s and Japan also bought a number.
After the war, ten of the US batch were converted back to HD.1 landplanes by the naval aircraft factory, but continued to be used as trainers aboard at Langley Field, with flotation bags and hydrovanes attached in front of the main wheels. One was employed in August 1919 for trials from a platform mounted on the battleship USS Mississippi.
HD.2 - (float-equipped)
Max speed, 113 mph (183 km/h).
Service ceiling, 15,750 ft (4800 m).
Range, 186 mls (300 km).
Empty weight, 1,091 lb (495 kg).
Loaded weight, 1,594 lb (723 kg).
Span, 28 ft 6.5 in (8,70 m).
Span upper: 8.7 m (28 ft 6.5 in)
Span lower: 7.4 m (24 ft 3.25 in)
Length, 22 ft 11.5 in (7,00 m).
Height, 10 ft 2 in (3,10 m).
Wing area, 195.9 sq ft (18,20 sq.m).