Astronaut Group 4 (The Scientists) was the fourth group of astronauts selected by NASA in June 1965. While the astronauts of the first two groups were required to have college and some advanced degrees, they were chosen for their experience as test pilots. Test pilot experience was waived as a requirement for the third group, but military jet fighter aircraft experience could be substituted. Group 4 was the first group chosen for research and academic backgrounds (Doctorate degrees) rather than pilot training, which NASA provided as necessary. Of the six, four had previous military experience, with Garriott also having completed the USAF Pilot Training Program; Schmitt, a geologist, walked on the Moon, while Garriott, Gibson and Kerwin all flew to Skylab. Garriott also flew on the Space Shuttle. Graveline and Michel left NASA without flying in space.