During November 1917 the squadron transferred to Hounslow Heath Aerodrome, and in March 1918 Major William Avery Bishop VC, DSO, MC, took command and carried out his orders to prepare and train for front line duties in France.

Equipped with the Sopwith Dolphin and later the Royal Aircraft Factory S.E.5A, it flew fighter patrols and ground attack sorties over the Western Front until the Armistice was signed.

During a patrol on 26 July 1918, accompanying Lt DC Inglis over the front line, Major Mannock failed to return, depriving 85 Squadron of its leader.

Besides Bishop and Mannock, the squadron had other notable aces, such as Malcolm C. McGregor, Arthur Randall, John Warner, Alec Reid, Spencer B. Horn, Walter H. Longton[5][better source needed] and Lawrence Callahan.

On the outbreak of the Second World War, the squadron moved its 16 Hurricanes to Boos as part of the Air Component of the British Expeditionary Force (BEF) 60 Fighter Wing.

Their primary role was to give support to the Fairey Battle and Bristol Blenheim units deployed around Rheims and to provide vital air defence cover for their airfields.

By 1 November 1939, another move saw the squadron posted to Lille Seclin and to maintain its patrols over the Channel, sections were detached to Le Touquet and Saint-Inglevert.

During one such patrol over the Boulogne area, the squadron scored its first victory of the war, when Flight Lieutenant R. H. A. Lee attacked a Heinkel He 111 which crashed into the Channel, exploding on impact.

The onset of winter proved to be an additional challenge as bitterly cold weather prevented flying, caused damage to aircraft and took its toll on the health of the airmen, who were living in fairly primitive conditions.

When the German invasion (Blitzkrieg) commenced in May 1940, No 85 Squadron found itself locked in a bitter contest with the Luftwaffe, and with attacks on its aerodromes commonplace there was no respite from operations.

After taking part in the first half of the Battle of Britain over southern England, the squadron moved to Yorkshire in September and in October following a change in role commenced night fighter patrols.

The collapse of the Warsaw Pact and the end of the Cold War period heralded wide sweeping changes in the United Kingdom's Air Defence needs.