The Dnepr rocket was initially developed for use as a ballistic missile. Therefore it was developed with an explosive charge that fired the rocket out of the ground and into the air, followed by the main engine ignition right above ground.
Graphic showing the launch sequence
Why did the Dnepr rocket still use the silo tube even after it became a commercial launcher? Wouldn't it be cheaper to stop using the ejection charges and just launch it from Baikonur?