The Type O made such an impression that for many years after the war any large aircraft in Britain was referred to as a "Handley Page", even getting a dictionary entry.

[1] Design work began shortly after the start of the First World War following meetings between Captain Murray Sueter, the director of the Air Department of the Royal Navy, and Frederick Handley Page.

[4] Coastal patrol adaptations of the abortive Handley Page L/200, M/200 and MS/200 designs were initially discussed but Sueter's technical advisor favoured a large seaplane for coastal patrol and dockyard defence that would also be capable of bombing the German High Seas Fleet at its base in Kiel.

The engines drove four-bladed propellers, rotating in opposite directions to cancel the torque, and were enclosed in armoured nacelles mounted between the wings on tubular steel struts.

The structure of the fuselage and flying surfaces was primarily spruce, with the spars routed into I-beams to reduce weight.

On reaching 70 mph (110 km/h), the tail unit began to vibrate and twist violently; the pilot immediately landed and an inspection showed severe damage to the rear fuselage structure.

Lanchester agreed that simple structural weakness was not the root of the problem and that resonance of the fuselage was the probable cause.

After completing acceptance trials, the second and third prototypes were retained at Manston to form a Handley Page training flight.

An initial order for 100 of the revised design, with Sunbeam Maori or Eagle engines, was placed on 14 August but cancelled shortly afterwards.

[18] As part of the Dardanelles campaign, an O/100 was flown 2,000 mi (3,200 km) from England to Mudros on the Greek island of Lemnos in the eastern Mediterranean by Lieutenant Ross Smith.

[19] It made night attacks against Ottoman Empire force, and supplied the small number of aircraft supporting the Arab insurgency being directed by T. E. Lawrence.

On the night of 3/4 July 1917, the Handley Page was used for an attack on Galata air base but the engines overheated and the crew turned back, jettisoning some bombs and dropping the others on an army camp near Bulair.

The next night, Constantinople was reached before midnight and they attacked the anchored battlecruiser SMS Goeben from 800 ft (240 m) with eight 112 lb (51 kg) bombs, and sank an Ottoman S138-class torpedo boat Yadigar-i Millet (Jadhigar-i-Millet).

On 30 September, (flown by John Alcock), it raided railway stations near Constantinople and Haidar Pasha but was forced to ditch in the Gulf of Xeros, after an engine failed.

[23] Another Handley Page was flown from England to reinforce the Palestine Brigade and served with 1 Squadron, Australian Flying Corps.

The Luxeuil Wing was disbanded in May to equip 10 Squadron RNAS for operations on the Western Front against the German spring offensive.

In September 1918, the 41st Wing was formed at Manston with the Handley Pages of "A" Squadron RNAS, for night bombing, and flown to Ochey in October.

[29] Eight O/400s were fitted to carry passengers and operated by 86 (Communication) Wing from Hendon, to provide transport between London and Paris for the officials negotiating the Treaty of Versailles.

[30] The first ever in-flight movie, 1925's silent The Lost World, was shown on a Type O, on the London to Paris flight by Imperial Airways in April 1925.

An early O/100, which had flown from Manston Airfield, developed engine trouble and landed behind German lines on 1 January 1917.

The Royal Air Force Museum Cosford has several relics, including pieces of fabric from an O/100 and various small O/400 components[36] and five O/400 wing sections which had been used as part of a shed roof in Flintshire until their recovery in late 2013.

[37] While there are no extant airframes, a detailed cockpit reproduction can be found at Stow Maries Great War Aerodrome, near Maldon in Essex.