Constituted as 344th Bombardment Group (Medium) on 31 Aug. 1942. Activated on 8 Sept. 1942. Equipped with B-26's and served as a replacement training unit. Moved to England, Jan.-Feb. 1944. Began operations with Ninth AF in March attack airfields, missile sites, marshalling yards, submarine shelters, coastal defenses, and other targets in France, Belgium, and Holland. Beginning in May, helped prepare for the Normandy invasion by striking vital bridges in France. On D-Day 1944 attacked coastal batteries at Cherbourg; during the remainder of June, supported the drive that resulted in the seizure of the Cotentin Peninsula. Bombed defended positions to assist British forces in the area of Caen. Received a DUC for three-day action against the enemy, 24-26 July 1944, when the group struck troop concentrations, supply dumps, a bridge, and a railroad viaduct to assist advancing ground forces at St. Lo. Knocked out bridges to hinder the enemy's withdrawal through the Falaise gap, and bombed vessels and strong points at Brest, Aug.- Sept. 1944. Attacked bridges, rail lines, fortified areas, supply dumps, and ordnance depots in Germany, Oct.-Nov. 1944.
Supported Allied forces during the Battle of the Bulge, Dec. 1944-Jan. 1945, and continued to strike such targets as supply points, communications centers, bridges, marshalling yards, roads, and oil storage tanks until April 1945. Made training flights and participated in air demonstrations after the war. Moved to Germany in Sept. 1945 and, as part of United States Air Forces in Europe, served with the army of occupation. Began training in A-26 but continued to use B-26 aircraft. Redesignated 344th Bombardment Group (Light) in Dec. 1945. Transferred, without personnel and equipment, to the US on 15 Feb. 1946. Inactivated on 31 March 1946.
Redesignated 126th Bombardment Group (Light). Allotted to ANG (Ill) on 24 May 1946. Extended federal recognition on 29 June 1947. Redesignated 126th Composite Group in Nov. 1950, and 126th Bombardment Group (Light) in Feb. 1951. Ordered to active service on 1 April 1951 and assigned to Tactical Air Command. Moved to France, Nov.-Dec. 1951 and assigned to United States Air Forces in Europe. Used B-26's for training and maneuvers. Relieved from active duty and transferred, without personnel and equipment, to the control of ANG (Ill), on 1 Jan. 1953. Redesignated 126th Fighter-Bomber Group.