Underground (Part 1)

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The Lost Mission maps
Underground 1 Title Screen.jpg

Underground - Sector 1: Mars City Service Sub-Level is the third level of The Lost Mission. The marine must find a keycard in order to go through security to deactivate the lockdown so he may proceed to the next sector to get to Exis Labs. This level is the first possible level to acquire a chain gun.


Spoiler Warning: Plot details follow.

To proceed further, the marine needs to disable security lockdown in Security Staton SL-3. To access the station, the marine needs a key card. The marine then goes though a whole bunch of corridors in a desperate hope of finding that key card. At some point he encounters a lift, upon activating which he's swarmed with trites. Anyway, it turns out the key card was on a catwalk of the same room as the door the marine needed to unlock. He unlocks the door, disables the security lockdown and leaves the part of Underground via a lift.

Spoilers end here.


Disable Local Security Lockdown
Acquire security station pass key
Return to Security Station
Use security terminal to gain access to service sub-levels.
Find Service Access to Exis Labs
Traverse service sub-levels to reach Exis Labs.





The monster count is the same on all skill levels.

Enemies Amount
Zombie 9
Machine gun Z-Sec 2
Shotgun Z-Sec 1
Trite 14
Imp* 15
Tentacle commando 1

* Three of the imps are crawlers.


The item count is the same on all skill levels.

Items Amount
Chain gun 1
Bullets (small) 2
Shells (small) 2
Shells (large) 2
Clip (small) 6
Clip (large) 1
Grenades 2
Ammo belt 3
Med kit (small) 8
Med kit (large) 3
Armor shard 22
Security armor 1
Key card 1

There are two health stations with 100 health each on the level.

Starting weapons[edit]

If the player starts this level via a console command, they will start with these items:

Items Amount
Shotgun 1
Machine gun 1
Bullets (large) 1
Shells (large) 2
Clip (large) 3
Grenades 2
Security armor 1

Locker codes[edit]

For the sources of the codes, see Doom 3 locker codes.
  • Storage locker #054 - Ammunition: 631. Contains: chain gun, ammo belt x2, med kit (small).


  • In Transfer Control, in the place where the player finds the key card, one can climb under the floor via a gap and find some health and armor there.