Competing with the United States Project Mercury, it succeeded in placing the first human into space, Yuri Gagarin, in a single orbit in Vostok 1 on April 12, 1961.

The Vostok capsule was developed from the Zenit spy satellite project, and its launch vehicle was adapted from the existing R-7 Semyorka intercontinental ballistic missile (ICBM) design.

The name "Vostok" was treated as classified information until Gagarin's flight was first publicly disclosed to the world press.

[1] Physicians from the Soviet Air Force insisted that the potential cosmonaut candidates be qualified Air Force pilots, arguing that they would have relevant skills such as exposure to higher g-forces, as well as ejection seat experience; also the Americans had chosen the Mercury Seven in April 1959, all of whom had aviation backgrounds.

[2] Chief designer of the Soviet space program, Sergei Korolev, decided that the cosmonauts must be male, between 25 and 30 years old, no taller than 1.75 meters, and weigh no more than 72 kilograms.

In March the cosmonauts were started on a daily fitness regime, and were taught classes on topics such as rocket space systems, navigation, geophysics, and astronomy.

[7] This group, which would be known as The Vanguard Six, was decided on May 30, 1960, and initially consisted of Gagarin, Kartashov, Nikolayev, Popovich, Titov, and Varlamov.

Firstly, during a centrifuge test of 8 g, Kartashov experienced some internal damage, causing minor hemorrhaging on his back.

Based on these results, a commission, supervised by Kamanin, recommended the use of the cosmonauts in the following order: Gagarin, Titov, Nelyubov, Nikolayev, Bykovskiy, Popovich.

[11] At this stage Gagarin was the clear favorite to be the first man in space, not only based on the exams, but also among an informal peer evaluation.

Despite the very large geographical size of the Soviet Union, there were obvious limitations to monitoring orbital spaceflights from ground stations within the country.

[14] For each ground station or tracking ship, the duration of communications with an orbiting spacecraft was limited to between five and ten minutes.

[15] At Korolev's suggestion, the media would call the spacecraft Korabl-Sputnik, ("Satellite-ship"); the name Vostok was still a secret codename at this point.

[17] The next mission, designated Korabl-Sputnik 2, was launched on August 19, 1960, carrying two more dogs, Belka and Strelka, as well as a variety of other biological specimens such as mice, insects, and strips of human skin.

[18] The spacecraft was only the second object ever to have been recovered from orbit, the first being the return capsule of the American Discoverer 13 the previous week.

[19] The success of Korabl-Sputnik 2 gave the designers confidence to put forward a plan leading to a human spaceflight.

A document regarding a plan for the Vostok programme, dated September 10, 1960, and declassified in 1991, was sent to the Central Committee of the Communist Party, and approved by Premier Nikita Khrushchev.

[21] It would be two weeks before work on the Vostok programme continued, and it was realised that the original target of a December crewed launch was unrealistic.

The only differences were that they would carry a single dog into orbit, a life-size mannequin would be strapped into the main ejection seat, and (unlike the crewed missions) they had a self-destruct system.

It carried the dog Chernushka into orbit, as well as a mannequin called Ivan Ivanovich, who wore a functioning SK-1 spacesuit.

[27] On March 23, before the next mission, an accident occurred during training which led to the death of cosmonaut candidate Valentin Bondarenko.

Like the previous Vostok 3KA flight, it lasted for only a single orbit, carried a mannequin and many animals, which included frogs, plants, mice, rats, and a dog, Zvezdochka ("Starlet",[30] or "Little star"[31]).