Gemini 4 carried the first American spacewalk, performed by astronaut Edward H. White II on June 3, 1965.
White left the spacecraft during the mission’s third orbit and spent about 20 minutes outside. He used a hand-held maneuvering gun to move around, although his movements were also controlled by a tether and the spacecraft’s orientation.
The event was a major milestone in NASA’s Gemini program, which developed techniques needed for future Apollo lunar missions. Gemini 4 also was the first American crewed mission to last several days, giving NASA experience with longer operations in orbit.
The Soviet Union’s Alexei Leonov had completed the first human spacewalk several months earlier, during Voskhod 2. Gemini 4 therefore represents the first American extravehicular activity, not the first spacewalk overall.