Doom 3 is set on the planet Mars in the year 2145. According to the game's backstory, the Union Aerospace Corporation (UAC) has grown to become the largest corporate entity in existence with near-unlimited funds, and has set up a research facility on Mars. At this base, the UAC are able to conduct research into several scientific areas, including advanced weapons development, biological research, space exploration and teleportation, outside of legal and moral boundaries. As the player progresses through the game, they learn that the employees on the base are unsettled due to a large number of incidents involving hearing voices, unexplained sightings and increasing cases of paranoia and insanity, often leading to fatal accidents with the facility's machinery. Rumors regarding the nature of experiments in the UAC's Delta Labs division are especially prevalent among the base's employees.
