How and why it happened -
By mid-1968, the Apollo Program was in full gear, though not all parts were proceeding equally smoothly.
Grumman, in particular, was having problems developing the Lunar Module, but North American Aviation had had the Command Module and Service Module ready for some time (they were sent up on the earth-orbit Apollo 7 mission, and proved usable).
NASA had originally set out a series of early Apollo missions for 1968-69 that involved docking maneuvres with both the CM and LM, but with the LM still incomplete, von Braun suggested something different - a trip to the moon with the full Saturn V rocket (it had been successfully tested Nov. 1967), minus the LM. The fact that it would be a great PR move, at a time NASA needed all the support it could get, helped to sell NASA management on the idea.
The biggest problem Mueller still faced was Apollo's slipping schedule and huge cost overruns. He had always thought the only way to resolve this, and achieve a lunar landing before 1970, was to reduce the number of test flights. Mueller wanted to use his "all-up testing" concept with each flight using the full number of live stages. This approach had been used successfully on the Titan II and Minuteman programs but violated von Braun's engineering concepts. The von Braun test plan called for the first live test to use the Saturn's first stage with dummy upper stages. If the first stage worked correctly then the first two stages would be live with a dummy third stage and so on, with at least ten test flights before a manned version was put into low earth orbit.The Saturn V program manager Arthur Rudolph cornered Mueller with scale models of Saturn and Minuteman. The Saturn dwarfed the Minuteman but Mueller replied, "So what?"
Eventually von Braun and the others were won over. As von Braun stated: "It sounded reckless, but George Mueller's reasoning was impeccable. Water ballast in lieu of a second and third stage would require much less tank volume than liquid-hydrogen-fuelled stages, so that a rocket tested with only a live first stage would be much shorter than the final configuration. Its aerodynamic shape and its body dynamics would thus not be representative. Filling the ballast tanks with liquid hydrogen? Fine, but then why not burn it as a bonus experiment? And so the arguments went on until George in the end prevailed."[8]
Mueller's concept of all-up testing worked. The first two unmanned flights of the Saturn V were successful (the second less so), then the third Saturn V put Frank Borman's Apollo 8 crew in orbit round the Moon on Christmas 1968, and the sixth Saturn V carried Neil Armstrong's Apollo 11 to the first lunar landing.
In an interview Mueller acknowledged what would have happened if all-up testing had failed, "The whole Apollo program and my reputation would have gone down the drain".[9]