In January 1944, Army Air Forces headquarters ordered the entire Air University night fighter training program to California to be headquartered at Hammer Field. Under the supervision of the Army Air Force School of Applied Tactics (AAFSAT) and the 481st Night Fighter Operational Training Group, night fighter crews were organized into Overseas Training Units and entered three phases of training. In all phases, Visalia AAF was used as a satellite training site. During this period, Douglas P-70 "Nighthawk" (heavy night fighter version of the A-20 "Havoc" light bomber) and Northrop P-61 "Black Widow" operated from Visalia AAF. It is known that the 425th Night Fighter Squadron was stationed at Visalia AAF for its entire training cycle from February until May 1944 when it was deployed to the European Theater at RAF Charmy Down, England as part of the Ninth Air Force.