In this chapter, the war against the Daemons is finally starting to turn in the humans' favour.
Head through two doors, grab some ammo on the right, then head for another door. Fight the Orks, who are scattered and confused without a leader. Chaos Space Marines will show up too once you have moved forward. Advance to the door on the other side once you've killed everyone and open it. Run forward into a checkpoint.
Run forward, open the door and start sniping as many Renegade Militia as you can. Run up to the next door and a short cutscene will play introducing the Tainted Psyker. It's best to take out these Psykers from a distance, as their attacks can be deadly and very quick. Once you've killed the Tainted Psyker and the reinforcements it summoned, go through the door.
Stack up on ammo and step into the arena-like room. Prepare for a tough fight against Renegade Militia. Once everyone's dead, head for the next door and go down the lift.
Enoch congratulates you on activating Invictus, but asks you to remove the mooring clamps holding the Titan in place. Turn around and go through the door on your right.
Prepare for a large-scale fight against a horde of Renegade Militia. After a while, some Bloodletter Daemons will join in on the fun, and make sure to give them equal treatment. Once everyone is dead, you'll have to fight a more powerful version of the Chaos Space Marine. Use Fury on him a lot.
Climb the stairs and through the door straight ahead of you. Then take the lift and listen to the short conversation before hitting another checkpoint.
Go through the door and grab a Storm Bolter from the support pod, then deactivate the mooring clamps in front of you. Now it's time to board the Titan. Go through the other door and fight the Chaos Drone. Head to the left of the next door and pick up the Servo Skull (Under Attack 1/3). Go through the door on your left and up the lift.
Run forward to end the chapter.