Tunnel Network

"Tunnel node used to supply passive defense structures."

- In-game description

The Tunnel Network is a strategically important structure that allows defences to have garrisoned AI which shoots at enemies automatically without players manning them. Defence structures such as the Foxhole, Pillbox, Gun Turret, Bunker, Sunken Pillbox, and Garrisoned House must be built within the vicinity of a Tunnel Network to have an active AI (About 40 meters). If passive defense structure gets disconnected from an active Tunnel Network, the AI will become inactive after 10 minutes.

Tunnel Networks can not be expanded in Skirmish mode.
 * Since Patch 0.16 they no longer decay.

Guide
Tunnel Networks must be connected to a Town Hall or Outpost in order to become an Active Tunnel Network. A closed hatch means that the Tunnel Node is connected to an Active Tunnel Network. An open hatch means that the Tunnel Network is not connected to a friendly Town hall or Outpost. Defences that are not inside an active tunnel network will not have AI, but are still mannable by friendly players.