The group was first activated at Key Field, Mississippi as the 404th Bombardment Group (Dive) with the 620th, 621st, 622d Bombardment Squadron and 623d Bombardment Squadrons assigned.
 The group drew its initial cadre from the 48th Bombardment Group, and was equipped with a mix of Vultee A-35 Vengeance and Douglas A-24 Banshee dive bombers and (briefly) Bell P-39 Airacobra fighter-bombers.
 In July, the group moved to Congaree Army Air Field, South Carolina, where, along with all other single engine dive bomber units of the Army Air Forces, it reorganized in August, becoming the 405th Fighter-Bomber Group.
Fighter groups were organized with three squadrons, rather than the four of bombardment groups, so the 623d Squadron was disbanded.

Between November 1943 and January 1944, most of the aircrew assigned to the group were detached for training on fighter aircraft and replaced by fighter qualified pilots, many of whom had been serving as instructors in various fighter training units.
On 22 March 1944, the group departed Camp Shanks, New York for the European Theater on board the MV Stirling Castle, arriving in Liverpool on 3 April.
The group was first activated at Key Field, Mississippi as the 404th Bombardment Group (Dive) with the 620th, 621st, 622d Bombardment Squadron and 623d Bombardment Squadrons assigned.  The group drew its initial cadre from the 48th Bombardment Group, and was equipped with a mix of Vultee A-35 Vengeance and Douglas A-24 Banshee dive bombers and (briefly) Bell P-39 Airacobra fighter-bombers.  In July, the group moved to Congaree Army Air Field, South Carolina, where, along with all other single engine dive bomber units of the Army Air Forces, it reorganized in August, becoming the 405th Fighter-Bomber Group. Fighter groups were organized with three squadrons, rather than the four of bombardment groups, so the 623d Squadron was disbanded.
Between November 1943 and January 1944, most of the aircrew assigned to the group were detached for training on fighter aircraft and replaced by fighter qualified pilots, many of whom had been serving as instructors in various fighter training units. On 22 March 1944, the group departed Camp Shanks, New York for the European Theater on board the MV Stirling Castle, arriving in Liverpool on 3 April.
137th Special Operations Group