Both the Soviet Union and the United States adapted existing military ballistic missiles to launch the first humans into space.
The Soviets used a modified R-7 intercontinental ballistic missile (ICBM) to launch Yuri Gagarin into space from Baikonur in the Kazakh Republic in 1961. The R-7, the world's first ICBM, had launched Sputnik, the first satellite, in 1957. An extra rocket stage was added atop the missile to convert it to a Vostok.
A modified U.S. Army Redstone launched Alan Shepard into space from Cape Canaveral in 1961. NASA also used a Redstone for Virgil Grissom's suborbital Mercury flight.
A modified U.S. Air Force Atlas ICBM launched John Glenn from Cape Canaveral on the first American orbital mission on February 20, 1962. NASA used Atlas rockets for the next three Mercury orbital flights.