Part 24

After shooting a marine, turn right at the ladder top to avoid being seen by marines in a nearby lift.

Use the first aid station if needed, then grab bullets and AR grenades.

Climb the next ladder and push the wooden crate to the left to crouch-walk past it on the right.

Carefully sneak-shoot the marine across the tracks to the right with the .357.

Break open the wooden crate for .357 ammo.

Crouch-walk down the ledge to the right of the tracks until you pass a dead marine and see a sandbag wall.

Shoot the marine behind the sandbag wall with the .357 as soon as possible; if he doesn't appear, try jumping across the track and moving around.

Move back along your ledge until you can see down the side track.

If vortigaunts are near the lowered barrier arm, shoot them with the pistol to potentially draw marine fire.

Move forward along your ledge to a spot where you can see marines in an area between the tracks to the left.

Crouch-walk back and forth between this spot and the vortigaunt sniping spot until fighting between marines and vortigaunts ceases.

Crouch-walk to the big gun behind the sandbag walls and use it to eliminate visible marines or vortigaunts ahead.

Warning: Marines may see you before you reach the big gun; consider sneak-shooting them with the pistol or .357.

Jump over the track to reach the marines' area, then crouch-walk forward slowly to check for vortigaunts across the next track.

If vortigaunts are present, shoot them with the assault rifle or .357 Magnum.

Break open boxes in the marines' area for supplies.

Jump across the track to where the vorts were, go up the stairs, and shoot two headcrabs and any hiding vortigaunts.

Crouch-walk along the walkway to the HEV station, being careful not to be seen by the marines on the lift below.

Return to the bottom of the stairs and jump back across the tracks to the big gun emplacement.

Find the stairs past the big gun, hop onto the side railing, and move up it.

When you can see the head of the marine past the stairs, use the .357 for a headshot (a shot that lands on the enemy's head, usually an instant kill).

Jump up to get another marine's attention, then quickly drop to the bottom of the stairs and wait for him to appear at the top to .357 him.

Past the top of the stairs, raid the radio area for health and ammo.

Go to the start of the nearby corridor, avoiding the left-side room with a marine.

Wait for the fight between vortigaunts and marines ahead to finish.

Move to a position where you can shoot vortigaunts to lure them back one at a time for easy killing.

Once all possible vortigaunts are killed, move into the corridor to load section c2a2c.

In section c2a2c, quickly finish off any remaining vortigaunts.

Go into the large side room and break the two boxes on the floor for .357 ammo.

Go along the walkway past the side room to some stairs.

Crouch at the top of the stairs and carefully crouch-walk to sneak-shoot the marine at the bottom with the .357, or toss a C4 satchel bomb to blow him up.

Warning: The marine may not be there due to the nearby conflict; watch for other marines near the bottom of the stairs.

Crouch-walk into the dark space under the bottom half of the stairs and break the crate for an armor battery and a floor grating.

Bash the grating and drop through the hole.

Move along until you find a dead marine; use your flashlight to look past him.

Quickly shoot the headcrab that appears.

Look around for supplies, including two more C4 satchel bombs.

Climb out of the secret area and crouch-walk slowly down the corridor to the right of the stairs to see who survived the fight above.

Quickly shoot any survivors.

Collect ammo from dead marines.

Jump across the tracks to find a large alcove with two crates for more supplies.

Warning: Surviving marines above the secret supply area may shoot you through the gratings; consider killing them first.

If your armor is less than 100%, return to the HEV station in the previous section to charge up.

Crouch-walk carefully along the ledge on the left side of the track leading away from this area until section c2a2d loads.

In section c2a2d, crouch-walk forward until you reach a stick-out pillar.

Beyond the pillar is a raised ledge with a red railing and three marines.

Warning: Quicksave before engaging the three marines on the ledge.

Crouch-walk very carefully to get into a position to sneak-shoot the marines with the .357.

After they are down, move forward to the next area.