Hanriot of France developed its single-seat, single-engine HD.1 fighting biplane of World War 1 (1914-1918) for service beginning in mid-1916. While passed on by the French Air Force it went on to stock the inventories of several foreign players of the period including the United States, the Kingdom of Italy, and Belgium. In due course, the same design was outfitted with floats and successfully tested to become the in-service HD.2 (detailed elsewhere on this site) and this form went on to be accepted by the French Navy and, to a lesser extent, the United States Navy. By the fall of 1917, the company was already hard at work on an all-new, twin-seat, single-engine biplane fighter - this to become the "HD.3".
A prototype was made ready before the end of the year and continued Hanriot's experience in biplane fighter development. The engine-of-choice became the Salmson (Canton-Unne) 9Za radial piston engine of 260 horsepower, this used to drive a two-bladed propeller unit at the nose. The biplane wing members were of equal span with single-bays, braced by a conventional parallel strut arrangement and the two of crew sat in tandem, open-air cockpits, the rear gunner's position raised slightly to afford better vision towards the rear of the aircraft. Armament centered on 2 x 7.7mm Vickers Machine Guns in fixed, forward-firing mounts (synchronized to fire through the spinning propeller blades) managed by the pilot and 2 x 7.7mm Lewis Machine Guns on a trainable mounting in the rear cockpit for the dedicated machine gunner. The undercarriage consisted of a conventional two-wheeled/tailskid arrangement for ground-running.
The French Air Service was sold enough on the design that it contracted for 120 in an initial production order during April 1918 when there was still a great need for new advanced fighters to match new German types in turn. Another batch order, this time by the French Navy, added 180 to the number though the Armistice of November 1918 limited the design's reach and production totals with just seventy-five eventually realized for the French Air Service inventory and just a few of the type to reach the French Navy.
Development of the design continued for a time later resulting in the "HD.3bis" night-fighter prototype - with thicker mainplanes and enlarged control surfaces - and the "HD.4", another one-off prototype having twin-floats fitted for on-water service. The related "HD.9 Ap.1" was a dedicated photoreconnaissance mount of which ten were evaluated by the French beginning in November of 1918.
In all, only about ninety or so HD.3 aircraft actually saw the light of day - the end of the war bringing an abrupt end to this capable biplane fighter. The only other notable operator of the series became the Kingdom of Italy where the HD.3 went on to serve with the Aeronautica Militare.
France; Kingdom of Italy
