Throughout the Apollo missions, one of the astronauts’ many training regimes took them poolside. Training underwater was one of the best ways to simulate a low-gravity environment, and it was much more pleasant than the zero-G training they did on an airplane (which they referred to as the “Vomit Comet”). Instead, they suited up and practiced maneuvers underwater at facilities like this, the Water Immersion Facility at NASA's Johnson Space Center.