French single-seat fighter biplane, prototype first flown 1916. It was designed by Pierre Dupont for the Sociote Anonyme des Appareils d'Aviation Hanriot and built by Hanriot at Billancourt, and was of sesquiplane configuration. The powerplant was a 110-hp Le Rhone 9 J rotary engine (120-hp Le Rhone 9 Jb on production aircraft) and carrying an armament of one synchronised 7,7-mm Vickers machine gun (although a few aircraft were later to be fitted with two Vickers guns). Tests proved it to be compact, manoeuvrable and with a good field of view. Although the HD.1 was accepted by the French government in early 1917, the huge contemporary production of the Spad 7 C1 precluded any production order for the French Aviation Militaire. Neither was the HD.1 considered to be a suitable replacement for the ageing Nieuport single-seaters.
However, the HD.1 did impress the Italian and Belgian authorities. It was adopted by Italy as the main Nieuport replacement, and went into licence production by the Societa Nieuport-Macchi at Varese. It seems that reports of 1700 being ordered from Nieuport-Macchi may have been exaggerated. Societa Nieuport Macchi delivered 125 to the Aeronautica del Regio Esercito in 1917, 706 in 1918, and a further 70 after the Armistice. 831 were received by the war's end, the balance coming from French production.
The HD.1 entered Italian service in mid-1917, serving in the Austrian, Macedonian and Albanian theatres. During the latter stages of the war they equipped 16 of the Italian air arm's 18 fighter squadrons, and some continued in service until 1925. Over nine-hundred were produced for the Italians and they used the type in greater numbers than any other fighter during the First World War.
The HD.1 was also adopted by Belgium to which country Hanriot supplied 79 fighters of this type from August 1917. The HD.1 continued in service in both Italy and Belgium into the mid-'twenties, and in 1921, Switzerland purchased 16 from Italian war surplus stocks and retained these in service until 1930.
Standard armament was a single 0.303-in (7.7-mm) Vickers gun, initially offset but later moved to a central position where the firepower was more effective, although the pilot's view was slightly impaired. Belgian orders, for French-built HD.1s, totalled 125, the first being delivered in August 1917. They were not instantly successful, but later gained popularity. One Belgian HD.1 was fitted with a single 11-mm (0.433-in) gun, which proved highly successful. Belgian HD.1s also served long after the war, some until 1926.
Small numbers were used by the French Aviation Maritime (naval air arm), with 130-hp Clerget 9 B engines and, on some, fin and rudder modifications similar to those of the HD.2. Switzerland purchased 16 HD.1s in 1921, and these remained in service until 1928.
Engine: 120 hp Le Rhone 9Jb.
Max speed, 115 mph (184 km/h) at sea level, 111 mph (178 km/h) at 6,560 ft (2 000 m).
Time to 3,280 ft (1000 m), 2.97 min.
Ceiling, 20,670 ft (6 000 m).
Range, 224 mls (360 km).
Empty weight, 983 lb (446 kg).
Loaded weight, 1,437 lb (652kg).
ROC: 894 fpm / 272 m/min
Span: 8.70 m, (28 ft 6.5 in) upper
Span: 7.40 m (24 ft 3.25 in) lower
Length, 19 ft 2.25 in (5,85 m)
Height, 9 ft 7.5 in (2,94 m)
Wing area, 195.9 sq ft (18,20 sq.m)