Level 2: Carrier
Find Valerie if possible
After youve managed to breach the walls of the carrier, swim through the passageway nearby and climb the ladder into the ships guts. Four or five mercenaries are wandering through the nearby hallways; theyll probably come running for you as soon as you open fire. Feel free to use a few grenades to empty out the hallway immediately next to the ladder, then utilize your M4 to clean out the rest of the rabble. One of the nearby rooms has a healthkit and a few flashbang grenades; pick these up and use them when you run across the two mercs whore packing P90 sub-machineguns, then off them and loot their corpses.
After you exit the boiler room where the P90 soldiers were, take a left into a little broom closet-ish room where you can pick up more health and armor. From there, move on into the torpedo storage room; dont be startled if one of the soldiers here turns on the alarm - you can just disable it after theyre all dead. Also, be alert for more troops who will rappel down the shaft in the ceiling of the room - you can get headshots fairly easily as they disengage from their rope.
Youll soon reach a ladder and will be able to head up to a higher level of the ship. Clear out the enemies nearby, and youll find a passage leading to the ships deck, but dont go outside until youve checked all of the nearby rooms for ammo.
Walking around outside is, or at least should be, slow going: theres plenty of mercs to worry about, including a few on the upper levels of the ship wholl shoot down on you, and one manning a stationary minigun at the ships bow. The MG merc will be difficult to see until youre exposed to his fire, so dont be afraid to hide behind something and lean out to snipe at him with your M4. Last, but not least, theres a semi-obscured soldier thatll blast you as you approach the ladder leading up to the second level here; approach it walking backwards and looking up, and you should spot him before he sees you.
Find the boat
Theres another short interior segment of the ship where you can restock your supplies before you head on to the really difficult fight on the ships deck. Make sure all of your weapons and reloaded and are set to automatic fire. Youre going to have two immediate problems upon reaching the deck: first, an attack helicopter will buzz up the side of the carrier, with a minigunner leaning out the side; and second, another soldier will be manning a mounted minigun on the other side of the carrier, ready to turn your body into small bits of goo. Oh, and theres also the 10 soldiers on the far side of the ship thatll start running towards you as soon as they see you, but theyre the least of your problems.
First off, hide behind one of the crates so that the mounted minigunner cant spot you, then start shooting away at the minigunner on the helicopter. After a full clip or two from one of your weapons, hell fall off of the helicopter and itll fly away, not to return. While its moving off, reload your M4, set it to single-fire mode, and lean around one of the crates to headshot the other minigunner. After both of those primary threats are dealt with, you can drop back down into the hole whence you came to restock on armor and health, if indeed you left those supplies where they were before you came up. Otherwise, just reset your weapons to automatic fire and start blasting away at the troops as they approach you. Theyll dash in and out from between the many boxes on the deck, so watch your corners as you proceed.
Some of the mercs will stay on the far side of the deck; switch back over to single fire and take them down before proceeding across the rickety bridges leading to the south end of the ship. Youll note your objective, a small propeller-driven boat, hanging from a couple of chains here. Shoot off the chains, and dive into the water (dont worry, youll survive).
Drive the boat east
Perhaps you should drive the boat east.