At the Gromov Flight Research Institute, a spacecraft simulator had been built, called the "TDK-1". Owing to the inefficiency of training all 20 cosmonauts in the simulator, it was decided they would select six men who would go through accelerated training. 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. Alexei Leonov recalls that these six were the shortest of the group of 20.