Constituted as 320th Bombardment Group (Medium) on 19 June 1942.

Activated on 23 June 1942. Trained with B-26 aircraft. Most of the group moved to North Africa via England, August-December 1942. Crews flew their planes over the South Atlantic route and arrived in North Africa, December 1942-January 1943. Began combat with Twelfth AF in April 1943 and operated from bases in Algeria, Tunisia, Sardinia, and Corsica until November 1944. During the period from April to July 1943, flew missions against enemy shipping in the approaches to Tunisia, attacked installations in Sardinia, participated in the reduction of Pantelleria, and supported the invasion of Sicily. Then bombed marshalling yards, bridges, airdromes, road junctions, viaducts, harbors, fuel dumps, defense positions, and other targets in Italy. The 320th bomb group supported forces at Salerno and knocked out targets to aid the seizure of Naples and the crossing of the Volturno River. Flew missions to Anzio and Cassino and engaged in interdictory operations in central Italy in preparation for the advance toward Rome. Received the French Croix de Guerre with Palm for action in preparation for and in support of Allied offensive operations in central Italy, April through June 1944. Received a DUC for a mission on 12 May 1944 when, in the face of an intense anti-aircraft barrage, the group bombed enemy troop concentrations near Fondi in support of Fifth Army's advance toward Rome. From June to November 1944 operations included interdictory missions in the Po Valley, support for the invasion of Southern France, and attacks on enemy communications in northern Italy. Moved to France in November 1944 and bombed bridges, rail lines, gun positions, barracks, supply points, ammunition dumps, and other targets in France and Germany until V-E Day. Received a DUC for operations on 15 March 1945 when the group bombed pillboxes, trenches, weapon pits, and roads within the Siegfried Line to enable a breakthrough by Seventh Army. Moved to Germany in June 1945 and participated in the disarmament program. Returned to the US, November and December.

Inactivated on 4 Dec 1945.