Mars City: Union Aerospace Corporate Division

"Marine? I can't believe you're still alive."

- Sergeant Kelly

Mars City: Union Aerospace Corporate Division is the third level of Doom 3. It is the same area as Mars City, but takes place after the demonic invasion. The marine is given his mission to link up with Bravo Team in this level. This is where the demo ends.

Summary
The player returns to Mars City to find the place in chaos. The sounds of battle can be heard coming from the walls, but at this point, most of Mars City has already fallen.

Fairly early in the level, the player encounters a survivor Roland who is hiding in the ventilation shaft near the elevator. Roland extends a ladder, allowing the player to climb into the shaft. He then urges the player to go get help.

The player uses the ventilation shaft to enter the Manifest Control Office, and from there, fights his way through Security Operations to the Infirmary. From there, he gains access to Marine Command and arrives back at Marine HQ. All the marines stationed there are dead, but a communications console is still working and has an incoming transmission from Sergeant Kelly, who is pleasantly surprised to see that you are still alive.

Sergeant Kelly informs the player that he is trapped in the Delta Complex and has decided to set up a command post there. He orders the player to link up with Bravo Team and help them send a distress call to the Earth Fleet. In order to reach Bravo Team, the player must head through Alpha Labs. Kelly also updates the player's security clearance, giving him access to the ACO section of Mars City.

With the aid of a surviving sentry bot, the player fights his way through the ACO area to the elevator. From there, he rides the elevator to the next level: Administration.

Characters

 * R. Roland
 * Sergeant Kelly
 * UAC announcer
 * Specialist Wilson (voice only)
 * S. Holmes
 * Sentry Bot

Enemies
Note: Includes only enemies that can be fought and killed. * The only one in the game.

Weapons/Items
There's also one health station on the level, with 100 health in reserve.

PDAs

 * Marcus Stanton: Found in Manifest Control Office
 * Marcus Caseon: Found in Infirmary.
 * Bill Tyson: Found in Marine Command, in corridor behind flaming pipe.
 * Duncan Mathews: Found in ACO Lift Junction. Requires going through a service access on the right of the room.

Cabinets/Door Codes
For the sources of the codes, see Doom 3 locker codes.
 * Cabinet #017: 347. Contains: med kit (large), security armor, clip (small), shells (small) x2.
 * Mars City Armory: 584. Contains: shotgun x2, machine gun x2, clip (large) x2, shells (small), med kit (large), security armor (2 on Recruit, 1 on Marine/Veteran).

Secrets

 * In the starting room there's a machine gun and some shards lying on a catwalk from which the player came from in the intro, but the staircase has collapsed so the player has to jump on a railing to get there.
 * When the player first meets the sentry bot, one can go back to reception where they got the PDA at the start of the game. There, one can access a nearby room with supplies by jumping through the window with missing glass panel.
 * In the last room, with the exit elevator in it, there's an vent shaft to the right from the entrance that can be used to access the second floor of the room, which contains a PDA that can be used to gain access to a locked office right before the elevator room, and some supplies.