Here is my walkthrough of the campaign, part 3, that shows exactly where to get this achievement.
- This is done after the new stern is attached.
- It requires climbing a large tower, lowering the module to the bottom of the tower, attaching it to a crane, and then lowering it down to the ship.
- To climb the tower, you push air into the lift, and to descend, you push water into the lift with the machine. This is also how you will raise/lower your ship as a submarine.