Unit repairs, base expansion
Mobile construction vehicle (with War Factory)
The Service Depot was a support structure used by both the Allied and Soviet armies during the Third World War and the Psychic Dominator Disaster. The purpose-built facility repaired friendly ground vehicles at a cost (dependent on how damaged the vehicle is) and remove Terror Droness. A service depot was also required to construct an MCV.
In a similar fashion, naval units could be repaired at the Naval Shipyard. In both cases, repairs would stop if the commander runs out of resources.
The service depot was considerably more important to the Soviets than the Allies. In the absence of a Tech Outpost or Tech Machine Shop, it was the only way Soviet battlefield commanders can repair vehicles (unless the vehicles are self-repairing, such as elite units and Apocalypse tanks). The Allies could use the mobile Engineer IFV to repair their ground units at no extra cost to the commander, although Terror Drones could not be removed in this way.