03/15/2017. Remarks by Johan Visschedijk: "The Hawker Horsley was notable in that it was the last wooden aircraft built by Hawker Engineering, entering quantity production in 1926 before the Kingston upon Thames, Surrey, factory facilities for metal construction had been completed. By 1927 the now-famous Hawker system of metal construction had been adopted and was incorporated to a limited extent in the Horsley Mk.II, while later Horsley Mk.IIs possessed an all-metal structure.

The Horsley was a large single-engine, two-bay biplane designed to Air Ministry Specification 26/23 which purported to lay down standard medium day bomber load requirements. First flown by Flight Lieutenant P.W.S. Bulman in 1925 the prototype Horsley, serialed J7511, was powered by a Rolls-Royce Condor III engine and featured radiators on each side of the fuselage some six feet behind the engine. This cooling system, however, was found to be unsatisfactory, with the result that the radiator was moved forward to the more orthodox "chin" position. The prototype was then delivered to the RAF for evaluation against other aircraft designed to the same Specification, namely the Bristol Berkeley, Handley-Page Handcross and Westland Yeovil.

In the meantime, however, the shortcomings of the 1923 Specification had been recognized and a new set of bomb load standards were laid down in Specification 23/25. Quite fortuitously, moreover, the following Specification, 24/25, also laid down load requirements, this time for torpedo-bombers. The maximum bomb load was to consist of either two 520 lb (236 kg), two 550 lb (249 kg), one 1,100 lb (498 kg) or one 1,500 lb (680 kg) bomb, though the latter type had not been produced since 1918. The torpedo called for was the standard naval ordnance type, weighing 2,150 lb (075 kg). An amendment issued later covered carriage of a torpedo weighing over 2,800 lb (1,270 kg).

The ease with which the Horsley could be adapted to carry these loads impressed the evaluation authorities sufficiently to prompt the Air Ministry in March 1926 to issue an initial contract for twenty Horsley bombers (based on the above pictured prototype). These were to be of wooden construction, but it is believed that in fact the composite metal and wood structure was introduced before the batch was completed.

Before the Horsley entered service with the RAF, a further number was delivered to Martlesham Heath at the end of 1926. Many minor teething troubles had to be overcome, including frequent tire bursts and a spate of engine cowling fatigue failures. The first RAF squadron received the Horsley in January 1927 and by January 1928 four bomber squadrons as well as the Night-flying Flight – also known as the Anti-aircraft Co-operation Flight – had received Horsleys, replacing Fairey Fawns and Vickers Vimys. As a torpedo-bomber the Horsley entered RAF service in June 1928.

The Horsleys were a considerable advance over the earlier machines, capable of carrying three times the bomb-load over greater distances. Powered by a Rolls-Royce Condor IIIA the two-seat bomber featured a Mark IIB bomb-sight operated by the observer, who adopted a prone position under the pilot's seat for bomb-aiming. Another feature of the Horsley, repeated on several later Hawker machines, was the ground-adjustable variable incidence tail plane, incorporated principally to cater for the widely varying load dispositions anticipated. Follow-up contracts had been received by the H.G. Hawker Engineering Company and in 1929 delivery to the RAF of all-metal Horsley Mk.IIs commenced.

In April 1929 Hawker had secured an order for six composite Horsley Mk.IIs to be built for the Greek Naval Air Service, and these aircraft were delivered to Greece by December. Five were used as torpedo-bombers, while the remaining aircraft became regarded as the Greek VIP transport; all were based at Tatoi.

Production aircraft were powered by the 665 hp Rolls-Royce Condor IIIA twelve-cylinder liquid-cooled V-engines driving a two-blade propeller. However, beginning in 1926 at least eight Horsleys were used testing a wide range of engines. Of the Rolls-Royce V-12 engines, four versions of the Condor, three versions of the Buzzard, one of the Eagle and four versions of the Merlin were tested. Furthermore were tested one version of the Napier Lion twelve-cylinder V-engine, one version of the Junkers Jumo 205 six-cylinder double-opposed diesel engine, as well as four versions of the Armstrong-Siddeley Leopard twelve-cylinder radial engine. Two-, three- and four-blade propellers were used.

A modified Horsley was used in an attempt to fly non-stop from the UK to India. The aircraft, serialed J8607, had a strengthened landing gear and by adding extra fuselage and wing tanks the fuel capacity was increased from 276 to 1,321 gal (1,045 to 5,000 l). Substitution of a larger fuselage tank resulted in the cockpit being moved further aft, while provision of a camp bed constituted the rather austere sleeping quarters. On May 20, 1927, Flight Lieutenants. C.R. Carr and L.E.M. Gillman took off from Cranwell, UK, but after 34 hr 45 min they were forced down in the Persian Gulf near Bandar Abbas, Iran, due to fuel starvation. With the covered 3,420 mls (5,504 km) a new long-distance record was set, which lasted for less than a day as later that day Charles Lindberg ended his flight from New York, USA to Paris, France, covering a distance of 3,590 mls (5,778 km) in 33 hr 39 min. Carr and Gillman spent a night on their ditched aircraft, the empty wing tanks no doubt served as useful buoyancy chambers, and were rescued the next day.

In January 1931 an all-metal Horsley, serialed S1452, was fitted with a trial target-towing installation that consisted of a fuselage-mounted target cable drum and wind-driven winch on the side of the rear cockpit. During 1931 and 1932 about a dozen Horsley target-towing conversions were carried out, mostly on the all-metal torpedo-bombers; the torpedo and bomb gear being retained.

During 1932 the RAF modified a single Horsley for Field Support duties. Known as the Horsley (Special Service) this was fitted with smoke screen laying gear and a third seat. The same year another Horsley was fitted with a twin float landing gear, it is believed that this installation was regarded as no more than a feasibility exercise.

Also in 1932 replacement of Horsley bombers by Vickers Vildebeests commenced and by 1935 the last of all Horsley had been withdrawn from RAF service."