[3] The first prototype was first flown at Brooklands in March 1925, powered by a 650 hp (480 kW) engine, and was delivered to the Aeroplane and Armament Experimental Establishment at Martlesham Heath on 4 May 1925.

[5] The Horsley's ability to cope with the increased loads required to meet these new specifications led to the design being favoured by the RAF, with an initial order of forty aircraft, consisting of ten wooden Mk Is and 30 Mk IIs of mixed metal and wood construction, being placed.

It had a crew of two, comprising a pilot and a gunner/bomb-aimer/radio operator, who had a .303 in (7.7 mm) Lewis gun mounted in a Scarff ring in the rear cockpit and a prone position for bomb aiming.

Two aircraft, known as the Hawker Dantorp and powered by Leopard II engines were sold to the Danish Government.

[9] The Danes also purchased a licence to build a further ten aircraft at the Danish Naval Workshops (Orlogsvaerftet), but these were not built owing to a shortage of funds.

[12] The Horsleys proved greatly superior to the Fawn, carrying up to three times the bomb load over greater ranges and at higher speeds, while also being agile for their size,[12] and were popular with their pilots.

Despite this it had covered a distance of 3,420 mi (5,500 km), which was sufficient to set a new world distance record, but was beaten in turn within a few hours by Charles Lindbergh, whose solo Atlantic flight between New York and Paris in the Spirit of St. Louis covered 3,590 mi (5,780 km)).