While a ground laser could track and engage a moving target, an airborne laser had the added difficulties of vibrations, beam propagation, and pointing a laser from an aerial platform. Development of the Airborne Laser Laboratory (ALL) became the centerpiece of AFWL's laser program in the 1970s. The ALL term was coined in 1972, and the ALL program began with Cycle I testing in 1973 and ended with the completion of Cycle III in September 1983. The ALL was a modified NKC-135, and the 4900th Flight Test Group was formed for aircraft operations. Laboratory testing occurred in the 400 area of Kirtland AFB and initial ground tests in hangar 1001, while the hangar at the Advanced Radiation Test Facility (ARTF) at the southeast corner of the runway was being constructed. ARTF was used for later ground tests that aimed the APT from the ARTF test pad to a target in the atmosphere in order to calibrate aircraft instruments in preparation for flight tests. Along with the five NKC-135, the 4900th FTG operated a fleet of five F-4Ds, one RF-4C, three NC-135As, five C-130s, and several A-37s, F-100s, and helicopters.