During World War II the group was an Eighth Air Force fighter unit stationed in England assigned primarily to RAF Duxford.

The group lost its P-38s, and most of its pilots, in February 1943 when they were assigned to the Twelfth Air Force for service in the North African campaign.

The group consisted of the following squadrons: From Duxford, the 78th flew many missions to escort Boeing B-17 Flying Fortress and Consolidated B-24 Liberator bombers that attacked industries, submarine yards and docks, V-weapon sites, and other targets on the Continent.

[4] The unit also engaged in counter-air activities and on numerous occasions strafed and dive-bombed airfields, trains, vehicles, barges, tugs, canal locks, barracks, and troops.

[1] In addition to other operations, the 78th participated in the intensive campaign against the German Air Force and aircraft industry during Big Week, 20–25 February 1944 and helped to prepare the way for the invasion of France.

The 78th Fighter Group received a Distinguished Unit Citation (DUC) for activities connected with the Operation Market-Garden combined ground and airborne attack through on the Netherlands in September 1944 when the group covered troop carrier and bombardment operations and carried out strafing and dive-bombing missions.

On 16 November 1948, the 78th was reassigned to Hamilton AFB, California where it was assigned to ADC's Fourth Air Force.

[1] With the outbreak of the Korean War in June 1950, the 78th Fighter Group was the only remaining ConAC F-84 unit with an air defense commitment.

The manpower shortage was worse, with only seven of the forty combat-rated pilots being available, the remainder being assigned Europe or combat duty in Korea.

By the end of 1951, the 82d FIS stood alert during daylight hours while the other two squadrons rotated night and foul weather duties.

There were not enough trained pilots and radar operators, and there were not enough maintenance personnel who knew the intricacies of the complex and troublesome Hughes E-1 fire control system.

[note 6] The group also became the host for Hamilton AFB and was assigned a number of support organizations to fulfil this mission.