09/30/2012. Remarks by Johan Visschedijk: "Modifications during 1917 of the basic Handley Page O/100 bomber, made by Chief Designer George Volkert, resulted in a new designation being applied: O/400 (retrospectively designated H.P.12). The main alterations were the removal of the nacelle fuel tanks and their transfer to the fuselage and the rearwards position adopted for the fin. The general shortage of Rolls-Royce engines made alternative power plants essential, substitutes being found in the 250 hp Sunbeam Maori and the 260 hp Fiat A-12bis. Cricklewood was the venue for the initial flight of the first 0/400.

The adoption of the day bomber in quantity was responsible during mid-1917 for the Air Board decision of July 23 to defer placing orders for new heavy bombers. Opposition to such a policy was such that only a week later, July 30, the matter was re-examined, with the result that O/400s, to the tune of one hundred, were ordered on August 14, 1917.

Meanwhile, proof had been forthcoming of the efficacy of night bombing, and the O/400 orders were increased substantially. By the spring of 1918, the O/400 had begun to appear in reasonable quantities and, for the succeeding months until the Armistice, made its name operating with the Independent Force of the Royal Air Force in long-range attacks on targets in Germany.

The pictured aircraft, assigned to No. 7 Squadron, was one of fifty (s/n D8301 to D8350) originally ordered from British Caudron (Contract AS.38340), but the order was transferred to Handley Page (Contract AS.18201) with British Caudron as main sub-contractor."