Screening of military service records showed 110 military officers that met these criteria. These 110 were to be called in three groups for briefings on the Mercury program. Of the first two groups of 35 called, 56 volunteered for further physical and psychiatric tests. This provided enough candidates and the third group was never even called for a briefing or asked if they would like to volunteer. Of the 56 tested, seven were finally selected (no objective way was found to reduce the seven finalists to six).

Of the seven astronauts, all eventually flew in space. Grounded due to a heart murmur, Slayton had to wait 16 years for his flight aboard the last Apollo mission. Glenn left for a career in politics after becoming the first American to orbit the earth, but returned to space aboard a shuttle over 36 years later in a NASA publicity stunt. Schirra was the only astronaut to fly aboard Mercury, Gemini, and Apollo spacecraft. Shepard was the only one to reach the lunar surface (after being grounded for a medical condition during the Gemini program). Grissom would die in the Apollo 204 ground fire.

	Carpenter	Malcolm Scott Carpenter. American Pilot Astronaut. Born 1 May 1925.
	Cooper	Leroy Gordon (Gordo) Cooper Jr. American Pilot Astronaut. Born 6 March 1927. Died 4 October 2004. First American to spend over a day in space.
	Glenn	John Herschel Glenn Jr. American Pilot Astronaut. Born 18 July 1921. First American in orbit. Oldest person in space.
	Grissom	Virgil Ivan (Gus) Grissom. American Pilot Astronaut. Born 3 April 1926. Died 27 January 1967.
	Schirra	Walter Marty (Wally) Schirra Jr. American Pilot Astronaut. Born 12 March 1923. Died 3 May 2007. Member of first crew to rendezvous in space.
	Shepard	Alan Bartlett (Al) Shepard Jr. American Pilot Astronaut. Born 18 November 1923. Died 21 July 1998. First American in space. Fifth person to walk on the moon.
	Slayton	Donald Kent (Deke) Slayton. American Pilot Astronaut. Born 1 March 1924. Died 13 June 1993.