During this turbulent period, new and updated weapons systems continued to join the USAF. The B-1B Lancer was delivered to SAC in record time, though with significant problems that would hamper its service career for some time. Stealth technology found its way to the ramps in the form of the F-117 Nighthawk fighter-bomber and the B-2 Spirit bomber. After the Space Shuttle Challenger disaster, AFSC helped restore the nation's space launch capability by quickly making available a family of new expendable launch vehicles such as the Delta II. Major gains were made in operational readiness rates through the Reliability and Maintainability (R&M) 2000 program.