The underground communications is located under the surface and is used for transferring objects from one building to another. The energy expenses for this process are very high so that only heavy objects that must be delivered fast are being transported there. Objects that courier can take, usually aren't transported through the underground as long as they get delivered to the right destination in time. But before the couriers existed, it was the only way to bring objects to another base.
A broken part of the underground communications can be accessed through the Volcano Sector's vent system during Mission 1 and Mission 2 from the Volcano Sector's main base. The reason for the access is an accident that occured there and the player has to evacuate cargo from the dangerous area. Otherwise mechminds aren't allowed to enter there if they have no special access for it.
Trivia
- Entering the underground communications for the first time, containers with goods and ammo will spawn at specified locations. Entering it one more time, the containers will disappear.
- Every time entering the underground communications, the map will be completely unrevealed.