AS-501 was the Saturn V’s first flight. At the time, it was the largest launch vehicle to ever attempt a flight. This mission was NASA’s first to use “all-up” testing, a decision that goes back to late 1963. George Mueller, the head of the NASA Office of Manned Space Flight at that time, was a systems engineer who previously worked on military missile projects. He recognized all-up testing was successfully used to rapidly develop the Air Force’s Minuteman ICBM program, and thought it could be used to meet Apollo’s schedule. Previously, the way Wernher von Braun’s team at the Marshall Space Flight Center, and the old NACA Langley Research Center engineers tested new rockets was by testing each stage incrementally. The Saturn V’s test program departed from the conservative incremental approach previously used by the Marshall and Langley engineers. It would be tested all at once, with all stages live and fully flight-worthy, including an Apollo command and service module (CSM). This decision dramatically streamlined the program’s test flight phase, eliminating four missions, but it required everything to work properly the first time. Apollo program managers had misgivings about all-up testing but agreed to it with some reluctance since incremental component tests would inevitably push the lunar landing mission past the 1970 goal.