...Like any other battles I had fought in before. [He says that with some weight behind it. Perhaps it was due to his experience, or maybe he was simply tired of it all]

Only, there's a higher uncertainty of where exactly the enemies are in these tunnels. With such dim lighting, it's easy to be ambushed by them. There aren't many path options either, so you have to take extra care not to get yourself trapped between the enemy on both sides. Those who break under pressure would not survive out there alone.