Swim along the pipe and shoot the fans that are in your way. Jump out of the water at the end, open the door and take the lift upstairs.

Enter the doors to gain access to the upper level, go into the chamber ahead and hit the computer console on your right - this will unlock the Main Bay Doors below.

Jump down and open the doors by pushing the control panel to the side of them. Go through and use the next control panel to access the lift. Open the right hangar bay door by pushing the nearby control panel, and proceed into the hangar.

Push the panel in the corner of the room to lower the lift. Hop on and go to the control room above. Go to the middle panel to lower the force field in front of the Skimmer. Use the left panel to open the left hangar bay doors. Follow the corridor until you reach the doors that house the Rear Entrance Force Field Controls.

Once inside, use the panel to deactivate the force fields. Open the doors and follow the corridor out. Enter the church, open the door on the right and walk up the stairs to the room at the top.

Approach the console by the force field, go down to the sanctuary and cross to the opposite door. Hit the control panel then go down the stairs to enter the church catacombs. Walk around to the back corridor and enter the door.