The Moon rocket platform was used by Yuri's forces to travel from their secret island in the South Pacific to the Moon, where Yuri has established his Lunar command center.
The following is based on the Soviet campaign for Yuri's Revenge and some details might contradict canon.
After the success of Operation: Escape Velocity, the Soviet forces discovered this launch platform on Yuri's secret island base. Analysis of the rocket's flight plan reveals that it has been programmed with a course to the moon. Following this lead, a Soviet Commander tracked Yuri's forces to the moon and destroyed the mad man's secret base there.