The official mission countdown began on Monday, April 10, 1972, at 8:30 AM, six days before the launch. At this point the SaturnV rocket's three stages were powered up and drinking water was pumped into the spacecraft. As the countdown began, the crew of Apollo 16 was participating in final training exercises in anticipation of a launch on April 16. The astronauts underwent their final preflight physical examination on April 11. On April 15, liquid hydrogen and liquid oxygen propellants were pumped into the spacecraft, while the astronauts rested in anticipation of their launch the next day.