The 372d Fighter Squadron was activated in early 1943 at March Field, California as one of the three original squadrons of the 360th Fighter Group, but moved on paper to Glendale Airport the same day. It operated as a Lockheed P-38 Lightning Replacement Training Unit (RTU). RTUs were oversized units which trained aircrews prior to their deployment to combat theaters. In January 1944 the squadron moved away from its parent group and established a separate RTU at Santa Maria Army Air Field, California.