 At Reading, the 148th Fighter-Interceptor Squadron (FIS) continued its air defense mission with the Mustang until 1956.With the end of the line for the Mustang in USAF service, the United States Air Force, in an effort to upgrade to an all jet fighter force, required Air National Guard Air Defense Command units to upgrade to jet-powered aircraft.The Reading Airport Commission and National Guard authorities found themselves in a conflict over the use of Reading Municipal Airport for tactical jet operations.