Ed White became the first American to leave his spacecraft in space. Tethered on a 4.6-metre (15 ft) line, he maneuvered using a hand-held oxygen-jet "zip gun" — the walk was meant to be shorter but stretched to roughly 23 minutes.
Before the spacewalk could even happen, the hatch latches jammed over Hawaii — McDivitt recognized the problem (a failed spring in the latch mechanism) from prior ground-test experience and helped force it open by hand. When White was reluctant to end the walk and Mission Control relayed through McDivitt the order "Get back in!", he replied with words that became famous: "It's the saddest moment of my life."
Getting back inside was no easier — reclosing the hatch after the walk took about twenty minutes and was a potentially fatal situation until both astronauts together secured it properly. Photographs from this spacewalk — White silhouetted against the Earth — remain among the most iconic images of the American space program.
From the flight transcript
"It's the saddest moment of my life."
NASA — Gemini 4 Mission Report · NASA — On the Shoulders of Titans: A History of Project Gemini · NASA Image and Video Library — full list on Gemini 4