NASA Photo ID: S79-36609
Date Taken: 09/18/79

Astronaut John W Young, crew commander for STS-1, prepares to be lowered into the water immersion facility for an underwater simulation of a contingency extravehicular activity (EVA) for securing payload bay doors aboard the Orbiter 102 Columbia. After donning his helmet and final readiness checkout is complete, Young will spend a period in the WIF to rehearse an extravehicular activity (EVA) that would be necessary in the event of failures in preliminary efforts to secure the large doors via remote control.

Source: NASA photo in my possession