Also... and I never see anyone else mention this... DOOM does not take place on Mars.
DOOM episode 1: Knee-Deep in the Dead takes place on Phobos. Episode 2: The Shores of Hell takes place on Deimos. Episode 3: Inferno takes place in Hell.
Doom 2: Hell on Earth takes place, as you might think, on Earth.
The whole plot of the first game is that humans are experimenting with teleporters between Phobos and Deimos, when Deimos mysteriously vanishes. To investigate, the player character is sent to Phobos, with the mission to make it through the teleporter to Deimos to see where it is. But upon arriving on Phobos, something is horribly wrong...
Right, forgot about the moons. I managed to confuse new and original doom in my mind. IIRC the humans didn't even invent the teleporters. They were already there.
They'd pull a Halo and have a doom guy romance arc for no reason. he'd pull his helmet off and it'd be like danial radcliffe or something (not a dig on Harry Potter, he's just not doom guy lol)