ED WHITE AND JIM MCDIVITT
Gemini 4 would be the first multi-day space flight by the United States, designed to show that it was possible for humans to remain in space for the length of time required to fly to the moon and back. A second objective for the four-day, 62-orbit mission was for Gemini 4 to rendezvous and fly in formation with the spent second stage of its Titan II booster rocket.
ED WHITE ON THE FIRST US SPACE WALK (EVA)
And although not originally scheduled for this mission, Gemini 4 would also see the first ever American Extra-vehicular activity (EVA, known popularly as a space walk). NASA moved up the original schedule after Aleksei Leonov on Voskhod 2 the previous March performed the first EVA ever, lest the US appear to be falling behind the Soviets again in the space race.
Gemini 4 would set a record for flight duration, and ease fears about the medical consequences of longer missions. It would also be the first use of the new Mission Control center outside Houston, which because of the flight's long duration, had to conduct three-shift operations.
(A note on Mission Control -- To garner the support of congress, President Kennedy had to have Vice-President Johnson behind him on the grand plan to get to the moon. Kennedy needed to placate the Florida electorate, and it was a decent place to launch spacecraft. Mission Control could also have been built in Florida, but Johnson wanted a piece of the action for his constituents, so that's why -- to this day, Florida handles launches and passes control to Houston after a launch clears the tower. Your tax dollars at work!).