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Delta Complex: Union Aerospace Research Division (also called Delta Labs Sector 5 in the autosave) is the twenty-first level of Doom 3. It is mostly a revisit (though there are a few previously unexplored areas) of various sections of the previous Delta Labs levels, with new and tougher enemies. The player will revisit portions of Delta Labs Level 1, 3, and 4.

From hereon, there will be no more zombies other than commandos. Ticks make their first and only appearance. Once more, the player loses their weapons on the journey back from Hell (with the exception of the Soul Cube) and must collect them all again. The player comes across a wounded Swann, who tells him to take his PDA and that Sergeant Kelly is working with the demons.


You begin in the Hell Knights duo room, with only the Soul Cube in hand. Grab the Pistol and Chaingun in the boxes near the closed door, then jump in the hole on the floor, picking up the Flashlight, the Grenades and some ammo in the process. At the end, you'll have to fight a Chaingun Commando. Pick his Chaingun, then take the rear door (the one which doesn't look like a sas). Kill the Tentacle Commando who lurks here, then pick up the Chainsaw. You can now enter in the sas-looking door. As usual, you won't be able to go back.

You are in the final area of Delta Labs Sector 3 : the room with the broken bridge. Run toward you and turn left to place yourself in the Delta Labs Sector 3's final teleporter's landing pad. It is a safe place to deal with the VERY long swarm of Ticks coming up. Just sit here and make one of the longest usage of the Chainsaw of the game, out of Ticks' reach. Once they are all dead, proceed on the other corridor ; the one which led to an inactive locked door in the Delta Labs Sector 3 level. It is now broken open. As you walk in the now Tick-ridden corridor, a Tentacle Commandos will teleport in front of you. Walk a bit more and a second one will teleport right behind you. I suggest to keep the Soul Cube and to kill them with the Chainsaw. There are a Plasma Gun, 5 Grenades and some ammo on a shelf right before the door. Then go in the elevator shaft, climb the ladder in it and crawl in the vent : you'll end above a tunnel of a previous level, precisely the second garage-like corridor of Delta Labs Sector 1, the one after the big generator room. From here, you'll revisit a portion of this level. You'll see a Chaingun Commando patrolling. Once again, once you jump in, you can't back. I suggest to jump without killing the ennemy for now.

Now you are one same ground as the Commando, unleash the Soul Cube on him. Be careful as the cube won't always target this ennemy... After killing the patrolling Chaingun Commando, walk a bit ; a Tentacle Commando will run at you from behind a crate. Walk a bit more and the wall in front of you will open, revealing an Arch-Vile, and spawning another Tentacle Commando from where you landed. Once the place is pacified, search around the crates to recover a Shotgun and an Adrenaline boost. Follow the path : a second Arch-Vile will come from the exit door, and a sempiternal Tentacle Commando will run at you from the point where you landed. Behind the door is a small lift room. Call for the lift and go on the floor level. Once on the lower floor, walk few steps and kill the Chaingun Commando coming from the front door. The next room has a little stair flight, with a Revenant behind the door atop. The door leads to a small room with an empty Health Station (perhaps it is related with how many you took and left in the first visit, in Delta Labs Sector 1) and an elevator for Delta Labs Authority. Take it and when you exit it, you are in a circular room, whith only one open door. Indeed, the now opened door was closed in the first visit, and the now closed one was open in the first visit. The door leads to the desk room. It has been previously visited, but this time a mortally wounded Swann lies here. Listen to him, take his PDA, and continue. The next corridor is overtaken by demonic growth, and there is a hole in the floor. Crawl in, get the ammo, armor and health there is in a shelf, and at the end, activate the maintenance ladder, which will open a trap on the floor.

The ladder leads to the "map room" of Delta Labs Sector 1, altough heavily modified and reduced, due to demonic growth taking over the place. As you arrive, the ladder retire and an Arch-Vile teleports near you, followed by a Tentacle Commando. Kill them quickly as a second Arch-Vile and Tentacle Commando duo appears rapidly. Once the place is pacified, collect the Medkit on a chair and the PDA near the map screens. It will allow you to reclaim a Rocket Launcher at the beginning of the next level. Swann's PDA allows to open the big CPU Complex door. There is a final Revenant to kill here, unless you return in the map room, which trigger an ultimate Arch-Vile to appear before you. There is a hidden Ammo Belt in the last room, as well as a monitor from which you can download informations about demonic rites, right next the exit door.


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