The 331st was converted to a Very Heavy (B-29) group in July 1944 and began training for deployment to Twentieth Air Force in the Pacific. The 211th Army Air Force Base Unit took control of the airfield. Casper AAF became part of Air Transport Command as a transit station for WASP pilots ferrying combat aircraft across the United States. The airfield was inactivated in March 1945, and on 30 September 1945 was turned over to the Army Corps of Engineers as surplus.