Handley Page suggested a land-based aircraft of similar size, and a specification drawn up around his suggestions was formally issued on 28 December 1914 for four prototypes. It called for a large biplane powered by two Sunbeam engines, which was required to fit in a hangar and would therefore have folding wings. It was to carry six bombs and have armour to protect crew and engines. The crew of two were to be enclosed in a glazed cockpit and the only defensive armament planned was a rifle for the observer/engineer. The designation O/100 came from Handley Page's sequence of using letters for each of their designs, with 100 for the proposed wingspan of the aircraft. The design was approved on 4 February 1915, with Rolls-Royce Eagle engines and on 9 February the contract was amended to include eight additional aircraft.