Gemini II, like Gemini I, was an unmanned mission intended as a test flight of the Gemini spacecraft. Unlike Gemini 1, which had holes drilled into its heat shield to ensure destruction during atmospheric reentry, the suborbital flight of Gemini II was executed with the primary intention of testing the spacecraft's heat shield.
The Gemini missions brought astronauts to the highest operational orbits to this day. And the higher the altitude, the faster the return.
A critical milestone in the progression of spaceflight advancement, a reliable heat shield on the Gemini spacecraft would ensure crew safety during reentry velocities far greater than those experienced on the previous Mercury missions.
Never actually making it into orbit, Gemini II achieved a maximum altitude of 171.1 km, and splashed down in the Atlantic Ocean, 3,422 km from the launchpad.