Constituted as 397th Bombardment Group (Medium) on 20 March 1943. Activated on 20 Arpil 1943. Trained with B-26's. Moved to England, March-April 1944, and assigned to Ninth AF. Participated in operations preparatory to the Normandy invasion by attacking V-weapon sites, bridges, coastal defenses, marshalling yards, and airfields, April-June 1944. Hit strong points in France on D-Day and and assisted ground forces throughout the remainder of the Normandy campaign by bombing fuel dumps, defended areas, and other objectives. Engaged in bombardment of German forces in the region of St. Lo during the Allied breakthrough in July.
After moving to the Continent in Aug., struck enemy positions at St. Malo and Brest and bombed targets in the Rouen area as Allied armies swept across the Seine and advanced to the Siegfried Line. Began flying missions into Germany in Sept. attacking such targets as bridges, defended areas, and storage depots. Struck the enemy's communications during the Battle of the Bulge (Dec. 1944-Jan. 1945) and received a DUC for a mission on 23 Dec. 1944 when the group withstood heavy flak and fighter attack to sever a railway bridge at Eller, a vital link in the enemy's supply line across the Moselle. Continued to support the Allied drive into Germany until April 1945. Returned to the US, Dec. 1945-Jan. 1946. Inactivated on 6 Jan. 1946.