Hanriot HD . 1 The Hanriot HD . 1 was a French World War I single - seat fighter aircraft . Rejected for service with French squadrons in favour of the SPAD S . 7 , the type was supplied to the Belgian and the Italian air forces with whom it proved highly successful . Of a total of about 1 , 200 examples built , 831 were in fact produced by Italian companies under licence . Development and production . The Hanriot company produced a series of pioneering monoplanes pre - war , but had settled down as a licence manufacturer , notably of Sopwith 1½ strutter s , when the HD . 1 was produced in 1916 . The type was a conventional fighter with the general characteristics of a typical Sopwith type , being strongly but lightly built , and combining clean lines with a light wing loading . In particular , it used the same “ 1½ ” ( or " W " ) cabane strut arrangement as the Sopwith two - seater . It had a flat lower wing , though the top wing had quite sharp dihedral . On the power of its Le Rhone rotary engine it was not outstandingly fast , but it was very manoeuvrable and proved popular with pilots as a safe and pleasant aircraft to fly . To maintain a competitive climbing and altitude performance it was usual practice to restrict armament to a single synchronised Vickers gun , although there was provision for a second gun , and one was occasionally fitted . In French built aircraft the gun ( or guns ) were fitted to the sides of the cockpit , and were accessible to the pilot without their butts being directly in front of his face in the event of a crash – an unusual but welcome feature , even if its origins lay in the form of the cabane struts . Italian - built versions , however , mounted a single machine gun centrally . The type was also produced by the Nieuport - Macchi company of Varese , Italy , which built almost 900 HD . 1s between 1917 and 1919 ; more than the parent firm . Operational history . The new type was ordered into production as a possible replacement for the Nieuport 17 , but became “ surplus ” when it was decided to replace the Nieuport with the SPAD S . 7 in the French air service . Some were supplied to the French Navy , a few of which were eventually passed to the U . S . Navy – some naval Hanriots were converted to , or built as , floatplane s with enlarged tail surfaces . The bulk of early production , however , was diverted to the Belgians , who notoriously had to make do with aircraft unwanted by their allies . With the Belgian fighter squadrons the HD . 1 proved surprisingly successful , and the type remained the standard Belgian fighter for the rest of the war . Willy Coppens , the top Belgian ace of the war was the most successful HD . 1 pilot . At least one of his machines was experimentally fitted with an 11mm Vickers machine - gun for use in balloon busting , something which Coppens excelled at . Most of his victories were balloons and many were claimed while flying various HD . 1s . The type was also supplied in small numbers to the Italians who manufactured it in quantity , and used it to replace not only Nieuports but also SPADs in their service . The type was considered ( by the Italians ) to be a better all - round fighter than even the SPAD S . XIII and it became the standard Italian fighter , equipping 16 of the 18 operational Italian fighter squadrons by November 1918 . Surplus Italian - built Hanriots were used by several countries postwar , including the Swiss . The U . S . Naval Aircraft Factory built ( or possibly modified / converted ) 10 HD . 1s in the immediate postwar years . These were mainly used as trainers , although they were also involved in experiments with takeoff platforms on warships – they could be fitted with twin guns , and at least one machine had a hydrovane and flotation bags of the type developed for the Royal Navy .