(1) This level is not terribly difficult because there is body armor right near the exit, allowing you to take your time and plenty of damage but still make your escape armored like a pro. There are 22 company soldiers here, and they can become quite annoying once most have made their appearance and begin to revive repeatedly as you move around; the most convenient thing to do is grenade them all (there are 3 very important powerup-toting exceptions). Exit the entrance doorway and move down the hallway, taking your first right. Grenade the 2 soldiers and explore the 4 rooms down this smaller hall.
(2) In the first pair of rooms you reach, the right holds 2 young dogs, while (left to right) lockers 2 and 3 hide an ID tag, battery, and med kit. The left room holds nothing.
(3) In the second pair of rooms, the right houses a young dog and an ID tag (lying on a desk); the left room also harbors a single dog, and the auto-map and a med kit are lying on a desk.
(4) As you leave this area, 2 new company soldiers materialize at the hallway junction. Kill them and stay right, where you will encounter another soldier around the corner. Take your first left down a short stairway into the dining hall and continue straight across up an identical stairway; kill the pair of soldiers here.
(5) Re-enter the dining hall and turn left; you will shortly encounter 2 soldiers, 1 just up the new stairway and 1 inside the kitchen. Activate the 2 switches on either side of the kitchen doorway and open the door to your right--a soldier awaits his fate on the other side.
(6) Kill him and move back inside the doorway; the middle locker of the trio to the right of the door holds an ID tag.
(7) Now proceed to an identical locker/door combination on the other side of the kitchen; the middle locker (when facing the door) yields a med kit, while the second locker (with the door on your right) holds a facehugger and ID tag.
(8) Now open the door and blow the crates directly in front of you, revealing a battery, facehugger, and med kit. The now-visible door behind the crates is not functional, so turn left down this hallway until you reach more crates and a switch. Activate the switch, blow the crates to reveal another door, and enter. Inside, the first 4 crates you see each hold a 'hugger, and behind those crates 4 young dogs lie in wait. Having dispatched them all, proceed to a second row of crates. These house 2 'huggers, while a single young dog lurks behind. On your way out, make sure you open 2 crates in this room that you probably missed on the way in; one holds a med kit while the other yields a special 10-up derm patch.
(9) Leave this room and stay to your right. As soon as you enter a long hallway, 2 soldiers will attack from a doorway to your left. Grenade them and continue down the long hall. You will pass a door hidden behind some crates on your left (to which you will return in a moment) as you move forward; keep going until you see another soldier near more crates. DO NOT GRENADE THIS SOLDIER and do not blow open these crates yet. Instead, pulse rifle the soldier and grab the grenades he coughs up. He will repeat this performance every time you kill and revive him, allowing you to exit this level with a full count of 20 grenades.
(10) Now backtrack to the crate-hidden door. Blow the crates (a seismic charge and facehugger lie within) and enter the door. Explode the crates directly in front of you and up the stairs; kill the emerging facehugger but don't go up the stairs. As you continue into this room, you will encounter more crates, 4 of which will release facehuggers. Kill 'em all, exit the room, and stay right.
(11) You will enter a room with several desks (don't miss the ID tag on one of them) and 2 switches. DO NOT activate the battery (large) switch just yet; instead, flip the small switch and blow the crates to the left of it to reveal another hall and a pair of night vision goggles.
(12) Activate the goggles and proceed forward. One or 2 dogs will attack before you reach the stairs. At the stairs, kill any reactivated 'huggers at the right-hand wall opening (this is the top of those stairs you ignored in this room earlier) and deal with the second young dog that will be here if he wasn't waiting for you farther back this hallway. Move forward and blow 2 'hugger-holding crates at the top of another stairway. Continue ahead and blow the secret wall you dead-end at. DO NOT GRAB THE BODY ARMOR JUST YET! There is also a clip and a shotshell in this secret hall, which you will be re-approaching from the other end shortly.
(13) Now reverse your route and go back to the battery switch you ignored earlier. Activating it opens the exit doorway and causes 6 company soldiers to materialize just outside the door. There will be 4 on the left and 2 to the right. Stay left out of this room, grenading the soldiers as you go. [BUG! There is one exception--DON'T grenade the second company soldier to emerge from the right. A sequence-specific glitch does not give you credit for all the ID tags you acquire when you play the level in this order, giving you a deficient score for MISSION at the end-of-level ASSESSMENT screen. You will need to revive this soldier and acquire an additional ID tag by killing him before exiting this level. If you are playing at the EASY or MEDIUM settings, you may need to vary your route to find the "right" sequence for this level before you can score the full 100%.]
(14) As you near the end of the hall, be careful NOT to grenade your buddy (the one that coughs up more grenades every time he expires). Use the pulse rifle if in doubt. At the exit doorway, 3 company soldiers emerge. The LAST one out is also a grenade-toter, so just pulse-rifle him. Now you can run up and down this hallway, repeatedly reactivating and killing these 2 soldiers, until your grenades are topped off at 20. [This is also when you will acquire the "missing" ID tag from the now-revived soldier.] NOW blow the crates here that you passed up earlier and kill the 2 facehuggers that emerge (had you blown these crates earlier, you would have revived these 2 'huggers every time you revived the grenade-yielding soldiers).
(15) You are ready to grab the body armor and exit. Open the door across the hall from the exit doorway and blow the secret wall inside. You can now grab the armor, clip, and shotshell.
(16) Move back to the exit door and make good your escape with a maxed-out armor and grenade count.