"Freedom Through Vigilance" is a five-volume (3,100 page) history of USAF Security Service ground and airborne operations. Volumes I through III document USAFSS ground units, and Volumes IV and V chronicle the history of USAFSS airborne reconnaissance. Volume IV covers the 6916th, 6988th and 6985th Security Squadrons plus the USAFSS "Navy" and airborne signals intelligence reconnaissance in World War II. Volume V addresses the history of the 6949th,...