The crazy man will finally let you through! Good thing he stops being crazy during a crisis. Follow along the tube and head through the door to enter the actual Marine Tube. It’s a pretty sight. Head down the tube. Feel free to talk to people along the way, but none of their conversations are important.
Continue until you reach the end and head through the doorway. Move through to the end of the gate. Talk to the Parasol Lady here and she’ll give you TM42 - Facade . Collect it and exit the gate.