"Training underwater for extravehicular activity (EVA)—popularly known as spacewalking—is now critical for preparing astronauts to work in weightlessness. But when cosmonauts and astronauts first ventured outside their spacecraft in 1965 and 1966, they had no such training. Spacewalking did not appear difficult, nor did space program officials think that underwater work was needed.

In the United States, it took Eugene Cernan’s June 1966 Gemini IX EVA to change attitudes. Fighting against his pressurized suit, while trying to do work without adequate handholds and footholds, Cernan quickly became exhausted and overheated. Only afterward did NASA Manned Spacecraft Center in Houston reach out to a tiny company outside Baltimore: Environmental Research Associates, Inc. (ERA). Funded by another agency center, it had been experimenting with EVA simulation in a rented school pool on nights, holidays, and weekends. That project became the foundation for Houston’s first underwater training facility. In parallel, NASA Marshall Space Flight Center in Huntsville, Alabama, had begun doing its own experiments. Together they effectively co-invented “neutral buoyancy training,” so-called because astronauts in weighted, pressurized suits have to be made neutrally buoyant to simulate zero gravity. (...)"