Watch the cutscene then choose to find the rotor. There's a Lancer and some ink bombs to the right, and a door on the left. You'll come out into a warehouse and be attacked by wretches. Just normal ones this time. Then go out the back door and you'll fight a group of therons and shriekers with a couple of troikas at the end. When you get closer, you'll see carts filled with old warheads. If you push them (before they explode), they will hit the wall at the end and destroy the troikas. Once cleared, exit to the left of the troikas.
Take the elevator in the warehouse (after stocking up on weapons). Outside you'll find an open area with a control room in the middle. On the roof of the control room is a Kantus; to the right of it is a Grinder. Scattered around are theron guards and shriekers. Try and clear out the Kantus and Grinder first, then quickly get rid of the shriekers as best you can and get to where the grinder was. A barge will or has already dropped of a rather large group on the far side of the platform and around the control room is a really good area to work from. Once you've cleared the area, make your way over to the maintenance bay.
Inside the Maintenance Bay, you'll find a half open ship with a Kantus on top and a Mauler inside and crawling with Theron guards. Again, kill that Kantus first. As you go down the ramp, of to the left is a door on the lower floor. If you go in and stick to the left wall, you'll see a red paper collectable. Clear the Mauler and the Theron, then grab the boomshield and use it to progress through the ship. Towards the other end you'll find stairs leading up. Take them, clear the last few theron from up here and then jump in the Loader. Use that to grab the rotor.
Use the Loader to open the next couple of doors and when you get outside you'll be attacked. Leave the loader back as far as you can and jump out. You'll have a variety of locust coming at you including a mauler (who will knock you out of the Loader) and eventually a Reaver. You need the Loader to survive. Hang back a ways and kill anything that moves and be sure to unload into the Reaver when it appears. Once clear, use the loader to open the next door. Continue on and dizzy will take the rotor and send you to fetch fuel.
Grab the sniper and fill up on ammo. Then head through the door and the next hallway. When you get to a big open area, stop and take cover at the corner of the hall. The first thing you want to do is pop the troika gunner in the head. Then look WAAAAAY in the back and get the Kantus. After that, the area should clear pretty easily. Climb over the island in the middle and then immediately right and loop back behind the shipping containers. You should find a COG tag. Go back and head out through the big door.
You'll come into a rather full shipping dock. After you encounter a couple of enemies, Jace should point you to a Silverback station. Check it out and jump in the Silver back. Use it to make your way up the dock. To move the ramp, you'll actually have to get out of the silverback for a second. After that, you can get back in and take it right up on the ship. There are to Kantuses here. Make sure you kill them first because the silverback has a habit of just downing the other enemies and in the rush to get them as fast as possible, they might not die and then be revived. Once you've cleared the ship, you can cross it and go to the control room to activate the crane.
Once that's done, grab the hammer of dawn that's sitting on the floor by the mainframe. Head back outside and you'll be attacked by Guards and some Reavers. Save the Hammer for the Reaver. Once the Bloodmounts come out, feel free to use it on them too if you can get a lock. Otherwise, just wait for them to come up and shoot their mask. It will stun them temporarily and you can usually kill them and then their rider if you're quick. Let them come to you though because the only way they can get up to the boat is over the ramp, use it as a choke point.
Now you just have to get back to the sub. Well sort of. The sub has fuel but you need to get it to the Dock. That's actually not too bad because the teams split up and one group always has a great view point for flanking. First your team will start high, and then you will go down and through the big doors and the other team will be up high. Then you can go up on the left side and into a control room with ammo for the last set of doors. In here immediately to the left of the door is a collectable on the ground and an infinite supply of ammo. By the window is a Vulcan Cannon. Use this and you'll clear the room very quickly.
The next area is rather tough. There's ammo on the left side between the two sets of cover. You will have to fight a couple waves of Theron guards, serapedes, and Armor Kantuses. There are four Armored Kantuses and they come one at a time. Marcus will recommend Explosives but you won't have enough if you use only explosives. What you need to do is hit him with a grenade to wound him. Then, when he stands up, he'll shout and his mouth will glow. That's when you want to shoot him in the mouth. It'll take about half a clip of lancer ammo before he goes down but provided you're not too far away, it should be almost a sure thing. And the Therons are carrying Torque bows if you're interested.
Once you've worked through that, head back and use the valve to flood the dock.
