Quote Originally Posted by Mysteltain View Post
T4 doesn't count for the achievement, being a single round room.
I'm pretty sure he was referring to the tank mounts achievement. There are a number of people who believe they can get it via T3, so they make 8 tank parties and continually run that for the tank mounts.

But you do get a mapping achievement for running T3 through to the end once, so there's that...