Mars City: Union Aerospace Corporate Division

MARS CITY - "Mars City is the gateway to all of Union Aerospace's Mars Base. All arriving personnel are processed here before moving to their assigned posts. Mars City houses the primary Marine Operations control room as well as the main administrator's office."

Mars City: Union Aerospace Corporate Division is the third level of Doom 3. It is the same level as Mars City, but after the start of the demonic invasion. In this level, the Marine must return to the Marine Command, where he is then given his mission to link up with Bravo Team in Alpha Labs, then have to travel through Administration. The Marine will encounter a handful of survivors (meeting one of them directly) as he can hear shouting and gunshots in his vicinity as they try to survive the demons' onslaught.

Notable features of this level include:
 * Picking up and using a Keycard; the pick-up sound is the same as in the original Doom.
 * Getting the Machine Gun from Z-Secs if you didn't pick it up in previous level.
 * First appearances of the Fat Zombie and the Flaming Zombie
 * First and only appearance of the Morgue Zombie
 * The infamous mirror scene.
 * The first escort with a Sentry Bot in combat.

AREAS IN MARS CITY:
 * Elevator
 * Maintenance
 * Ventilation Shaft
 * Manifest Control Office
 * Manifest Control Entrance
 * Reception Processing
 * Conference Room
 * Hallway
 * Sec Ops Processing
 * Security Operations
 * Sec Ops Junction
 * Infirmary Access Junction
 * Operations Station
 * Infirmary
 * Infirmary Observation Room
 * Marine Command
 * Combat Preparation
 * Marine Headquarters
 * Marine Command Access
 * Command Access Junction
 * Common Area
 * Restroom
 * Central Access
 * Central Access Junction
 * Mars City Reception
 * ACO Access Junction
 * ACO Offices
 * ACO Lift Junction
 * Service Access

PDAs

 * Marcus Stanton
 * Mark Caseon
 * Bill Tyson
 * Duncan Mathews

Characters

 * S. Holmes
 * Thomas Kelly
 * R. Roland
 * UAC announcer
 * Specialist Wilson

Statistics

 * For cells of the form x/y/z, x corresponds to Recruit difficulty, y to Marine, and z to Veteran/Nightmare.
 * Items that can only be acquired by using console commands are excluded.

Cabinet/Door Codes

 * Storage Cabinet #017: Supplies - 347
 * Weapons Storage - 584 ; in order to get it, right after exiting infirmary, there is a corridor with a path blocked by flames pouring of a pipe, and a Medkit next to it. You have to run through it to access to a secret zone and get the PDA with this code, and then back, traversing the flame again.

Trivia

 * In the beginning of the level, when the player enters a small room next to Central Access Junction to pick up a keycard, an Imp will be seen in the window tearing off the skin of a Fat Zombie. Once the player enters the Central Access Junction to confront the Fat Zombie he saw earlier, its skin appears intact.