Drive the cart until you come to the blockade. Talk to the security guard. He'll tell you that you need to launch the satellite to put an end to the invasion. The military has shut it down, and you have to remedy the situation. Get off the cart, grab the first aid kits, and flip the switch to raise the blockade. Before getting back on the cart, run into the other room and shoot the Barnacles on the ceiling. Then drive the cart onto the lift.

The lift will go down. Move forward through the flooded tunnel. Don't fall off - that water is electrified. At the top, watch for the HEV power canister on the right. Stop the cart, get off, and pick it up. Get back on the cart and continue forward. You'll pass an intersection with a crane blocking the track to the left. Kill the Houndeyes and move on. Leave the track switchers alone for now. Follow the track along until you come to a small alcove with a Bullsquid and a dead soldier. Stop the cart, kill the squid, and jump onto the platform. Get the first aid kit. The crates at the end of the room contain an HEV power canister and a Grenade. Get back on the cart. As you move forward, watch out for the Barnacles on the ceiling above.

At the next alcove, kill the squid. Stop the cart and get off. There's a stairway here, with a health dispenser at the bottom. Climb the stairs. Use a Grenade to take out the crates. If the Grenade didn't take out the turret beyond, dispose of it quickly. Flip the switch in the control room to move the crane. Climb back down to the cart and continue forward. When you see the track switcher, shoot it so that you see the arrow pointing left. The cart will move to the track previously blocked by the crane.

You'll come to a lift. Some soldiers are waiting above. The best tactic is to wait until the lift begins to ascend, then jump off. Climb up the ladder and take out the grunt on the first level. There's a health dispenser and some ammo here. Climb the ladder to the second level. Carefully take out the grunt waiting on the tracks ahead, then jump onto the cart and move forward.

Around the first bend, there will be a serious firefight with some soldiers. Deal with the one on the right, then use the barricades for cover. If you want, you can use the mounted gun to take out the rest. On the wall is a switch. Flip it to raise the blockade on the track. Before moving on, do a little exploring.

Up the stairs near the barricade, numerous soldiers are fighting some Alien Slaves. Clear out the stragglers (and beware of the soldier hiding behind the wall in the office at the top of the stairs). Follow the hallway around until you reach another staircase. A soldier waits at the bottom. The hallway goes left and right. To the left, you'll come to a part of the track blocked by two blue lasers. Shoot the emitters to remove the threat. Move back and head the other way down the hall, where you'll find some soldiers fighting some slaves. Finish off whoever is left.

Before going back up, look under the stairway. Turn on your flashlight and break the crate to find a power canister. Break the grate and drop down to find some first aid kits and ammo guarded by some Headcrabs. Now go back up and get back to the cart. Jump across the track and to the other side, where the soldiers have killed some Alien Slaves. There's a switch here you must flip to lift another blockade. Head up the stairs. Fight your way to the back room, where you'll find an HEV power dispenser.

Go back down, board the cart, and move forward.

At the end of the track, you'll encounter some soldiers. You may want to stop the cart just before the end and take them out with a Grenade. Search the bodies, then jump across the tracks to the hallway. Fight the slaves and the soldiers and keep moving. You'll come to a boarded door; behind it is a security guard and some crates. In the room across the hall, you'll find a health dispenser hidden behind some crates. But watch out for the Headcrabs falling from the ceiling.

At the end of the hall, a huge barricade protects a soldier firing a mounted gun. Use the crates as shields and make your way across the tracks, out of the gun's range. Back where the graffiti says "Surrender Freeman," you can toss a Grenade into the barricade to kill the soldier. Go through the blast door and crawl under the blue lasers. Kill the soldier on the walkway below, then climb down the ladder. Go through the blast door. And search the crates in the office for some Magnum rounds. There's also an HEV power dispenser hidden behind the office.

Get on the freight cart and move forward.

Duck under the red lasers to avoid having to deal with the turrets beyond. Near the third turret, you'll see a door. Jump off and go in to find some ammo, along with a Bullsquid, a Barnacle, and some Headcrabs. Get back on the cart and keep moving. Around the next bend, a rocket launcher will begin firing at you. Strafe back and forth on the cart to avoid its fire. Take out the soldier just beyond the rocket launcher.

Blue lasers block the tunnel, so set the cart to a slower speed and jump off. Follow behind it on the ledge next to the track. It will activate the lasers and you won't get hurt. Jump back on the cart when the path is clear.

Jump off at the next area, which is teeming with Alien Slaves. Kill them all, and use the health dispenser. Go through the hallway until you come to a stairway blocked by some crates. Jump over the crates and head up. Kill the soldiers and flip the switch to raise the blockade. There's an HEV power dispenser here. Go down to the track. Don't get back on the cart you rode in on - that track leads to a deadly trap. Jump on the other and move forward.

Stop well before you get to the next blockade. There's a large group of soldiers nearby, guarding the switch. Try to take them out without entering the room yet; there's a large gun waiting around the corner. Run in and climb the ladder, making your way next to the gun. Throw a Grenade into the barricade to take out the gunner. Use the dispenser, flip the switch, and get back on the cart.

Stop the cart before you get to the lift. There are numerous soldiers, and it's easier to fight them on foot. Climb up and search the crates. Walk around the small ledge of the lift shaft to find the items nestled in the open grate. Once the area is clear, climb down to the cart and move it onto the lift.

At the top, some stray electric surges sporadically block the path. Stop the cart before each one and time your movement forward so you don't get hurt. Set the cart on its slowest speed, jump off, and follow. It'll activate the laser traps waiting around the next corner. Get back on and duck under the boxes in the next room. At the blockade, two soldiers will be waiting. Take them down and flip the switch.

Stay down through the next room and the next tunnel, avoiding both the crates moving overhead and the rocket volleys being fired your way. Take out the soldier as you pass the rocket launcher. The next room has more stray electricity. Time your movements so you don't get hurt. At the track switcher, shoot it so the arrow is facing forward. You're about to hit the end of the line.

Get off the cart and toss a Grenade down the ladder chute to take out the blue laser below. Climb down, and jump off the ladder to avoid activating the turrets. In the room at the bottom, you'll find some Grenades, a health dispenser, and some Zombies. Move down the track when you're finished here. Around the bend, you'll find a big gun. Use the crates and barricades to avoid its fire. Take out the soldier and then kill the gunner with a Grenade. Search the crates and head up the stairs.

Outside, listen to the soldiers talk about you, then kill them. Watch out for the hidden turret on the wall to the left. Head toward the blast door, and open it with the keypad. You'll have to fight three more soldiers to make it to the next blast door. There's a big gun in the corner to your left that will help, along with some first aid and Assault Shotgun shells. Once the soldiers are gone, go in. Those red lasers blocking the stairway are lethal. Use the metal crates to make a ladder up to the ledge, then jump up, avoiding the stairs altogether.

Through the door you'll see two more soldiers. In the computer room, you'll find a health dispenser. Get to the control room and push the big red launch button. After the rocket has launched, head out of the control room and back outside. Go through the big blast doors and head through the huge door, which is now open.

Climb down the ladder; you'll find plenty of supplies in the crates, including some Satchel Charges. Get on the cart and start moving forward.