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Gear Tunnel is an underground railway tunnel seen in Armored Core 4 and Armored Core: For Answer.



The Gear Tunnel is a series of underground railway lines meant to allow the passage of large freight trains between colonies. It is presumably connected to Anatolia, as the Juggernaught Ursragna attempted to use this underground system to reach and destroy the colony.


  • The trains seen within the Gear Tunnel in Armored Core 4 are much larger than modern equivalents, occupying a pair of railway tracks side-by-side.
  • The Gear Tunnel is shown to to more complex than a single passage in Armored Core: For Answer, where it appears in the mission "Elyminate Procyon" as a web of smaller tunnels.