Doomsday of UAC

Doomsday of UAC (commonly known by its filename UAC_DEAD) is a single-level PWAD designed by Leo Martin Lim. As part of their 10 Years of Doom feature, Doomworld named it one of the ten best WADs of 1994.

One of the first ever fan-made Doom mods, UAC_DEAD features an attempt at creating realistic-looking vehicles and environments. It contains a replacement sky graphic, and uses careful flat and texture choices in places to simulate colored lighting. It also includes the first known instance of the self-referencing sectors trick, used to create both invisible stairs and an invisible chamber enclosing a cyberdemon.

UAC_DEAD was originally released June 23, 1994. It also appeared on Maximum Doom as UAC_DEAD.WAD, as UAC_DEA2.WAD, and as E1M4 of DEATHM2.WAD.

Secrets

 * 1) Of the three trailers closest to the northeast of the first area, the middle one can be opened from the east.  At the other end is a chaingun; approaching it will cause the door to close.  Press the switch behind it, and the sides will drop to release monsters.  In the northern trailer is a partial invisibility, and in the southern one is a switch that opens the door.  Enter the southern trailer to trigger this secret. (sector 82)
 * 2) After pressing the switch that leads to secret #1, another trailer to the south of the three trailers will open to release monsters.  At the end of this trailer is a medikit.  This trailer counts as a secret.  (sector 62)
 * 3) In the middle of the first area, the top halves of multiple crates will be floating in the sky; beneath them is a wall of fire.  Run through it to find a supercharge. (sector 109)
 * 4) On the third step from the stop of the stairway leading to the underground parking lot, open the wall at its western side.  This will reveal a tunnel that leads behind the UAC sign, where you can get a supercharge and megaarmor. (sector 351)
 * 5) To either side of the conveyor belts, there is a pair of supercomputers.  Both of them have sections that stick out diagonally from the wall.  Behind those of the southern supercomputer, press the wall at a spot that coincides with the middle of either one of those diagonal parts.  At either of these locations, a secret door will open, leading to a reactor room built in the shape of the UAC logo. (sector 193) Among the loot you can recover from this room are four medikits, two boxes of shotgun shells, three energy cell packs, two radiation shielding suits, a computer area map, a chainsaw, and a plasma gun.
 * 6) In the red rock cavern, just after the exit to the complex is sealed off, there is a section of red stone in the middle of the eastern wall.  Open it to find megaarmor, as well as a switch that opens access to the complex early. (sector 277)

Bugs

 * Playing this map on UV exceeds the savegame buffer size in Doom v1.2.
 * If the player somehow manages to slip by the first baron of Hell, they can become trapped in the red key room.

Current records
The records for the map on the Doomed Speed Demos Archive are:

Things
This level contains the following numbers of things per skill level:

Technical information
This map occupied the E1M8 slot in order to use the special tag 666 twice, exploiting a peculiarity of Doom's handling when more than one type of boss monster is present in the map. This peculiarity was changed in Ultimate Doom, and as the Doom source release inherited the change, the map is unplayable in many modern source ports due to the red key being unobtainable. Chocolate Doom, Doomsday and PrBoom have option settings which allow the trick to operate as intended, and ZDoom and GZDoom identify the level through its checksum and automatically apply the correct compatibility flag.

Inspiration and development
The sky texture in this level is taken from Josh Fallon's "Nightfall" (NIGHTFAL.WAD).

Trivia

 * The invisible stairs are meant to be reminiscent of the film Indiana Jones and the Last Crusade.
 * John Romero has specifically named UAC_DEAD as the first "really cool" user-made PWAD he ever played.