Gemini 4 carried out the first American spacewalk in June 1965.
Launched on June 3, 1965, Gemini 4 carried James McDivitt and Edward H. White II. During the mission’s third orbit, White opened the hatch and floated outside the spacecraft for about 20 minutes, connected to Gemini 4 by an umbilical line.
White used a handheld gas-gun device to maneuver, although the device’s propellant was eventually exhausted and he had to pull himself back toward the spacecraft. His spacewalk demonstrated that astronauts could work outside a spacecraft, an ability essential for later lunar missions and space-station construction.
Gemini 4 was not the first spacewalk overall. Soviet cosmonaut Alexei Leonov completed that milestone during Voskhod 2 in March 1965. Gemini 4 also lasted four days and helped NASA study the effects of longer-duration spaceflight.