The flight of Gemini 4 in June 1965 was conducted barely four years after the first Americans flew in space. It was a bold step by NASA to accomplish the first American spacewalk and to extend the U.S. flight duration record to four days. This would be double the experience gained from the six Mercury missions combined.This daring mission was the first to be directed from the new Mission Control at the Manned Spacecraft Center near Houston, Texas. It also revealed that:
- Working outside the spacecraft would require further study.
- Developing the techniques to rendezvous with another object in space would not be as straightforward as NASA had hoped.
- Living in a small spacecraft for several days was a challenging but necessary step in the quest for even longer flights.

Despite the risks, the gamble that astronauts Jim McDivitt and Ed White undertook paid off. Gemini 4 gave NASA the confidence to attempt an even longer flight the next time. That next mission would simulate the planned eight-day duration of an Apollo lunar voyage. Its story is recounted in the next title in this series: Gemini 5: Eight Days in Space or Bust.