Gemini 4 (officially
Gemini IV) was the second
manned space flight in
NASA's
Project Gemini, occurring in June 1965. It was the tenth manned
American spaceflight (including two
X-15 flights at altitudes exceeding ).
Astronauts James McDivitt and
Edward H. White, II circled the Earth 66 times in four days, making it the first US flight to approach the five-day flight of the
Soviet Vostok 5. The highlight of the mission was the first
space walk by an American, during which White floated free outside the spacecraft, tethered to it, for approximately 20 minutes. Both of these accomplishments helped the United States overcome the Soviet Union's early lead in the
Space Race.