The Soyuz first stage is a medium sized first stage part that is a part of the Soyuz rocket. It is designed to be joined to the Soyuz 2nd Stage. It is the smallest of the Russian rockets in the game. Note that Boosters cannot be attached to the sides.It is similar to the Proton First Stage in that it has pre attached boosters.
In career mode the part costs $10,000,000.