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At some point, the Brotherhood of Steel occupied the tunnel, using it as a checkpoint to stop the raiders from occupying it and to provide quick passage under the Savage Divide. After the fall of Fort Defiance and the destruction of the Brotherhood's presence in Appalachia, the tunnel was occupied by the Scorched, and the Fire Breathers sent a team to destroy the west entrance, but they were unsuccessful.
A long straight tunnel running East-West with a service/storage area (crafting stations) halfway through. The storage area requires a key which can be found in the East extension tunnel starting from this storage area.
- Cominsky's code - Note, on Sgt. Cominsky's corpse, near the end of a side tunnel with railroad tracks running south that are at a right angle to the tracks that run through the tunnel.
- Orders from Melody - Note, on Sgt. Allemane, Cominsky and Holstein's corpses.
- Scattered journal pages - Six notes, scattered throughout the tunnel.
- Isaac's message to the Sloth - Holotape, on a terminal station in the room with the catwalks.
- Big Bend Tunnel door key - On a corpse sitting on an excavation machine. Go south from the cavern with the buildings using the same route as for Sgt. Cominsky.
- Random bobblehead - On a filing cabinet across from a terminal, past the locked blue double doors.
- Random magazine - In the room with the catwalks, on a desk.
- Fusion core - In a fusion generator in the storage room with the mole rats.
- Power armor chassis with random parts - In the storage room, across from the fusion generator inside the locked area tha requires the Big Bend door key.
The locked area can be accessed without the key by climbing a series of boxes and jumping over the railing onto the catwalk that goes over the tracks.
The Big Bend Tunnel appears only in Fallout 76.