Like its sister ship, the Phobos, the Deimos is covered in defenses; its back and underside bristling with cannons and guns of various descriptions, its landing bays home to an entire wing of fighters and bombers, its port and starboard sides lined with row upon row of launch tubes carrying hundreds (if not thousands - precise numbers are unavailable) of Drop Pods and the Marines contained within, to be fired like torpedoes at the invasion target.
It is a highly versatile ship, capable of performing multiple roles; serving as a command and intelligence center, air and spacecraft carrier, troop and supply ship, mobile weapons platform and invasion launchpad. Also like its sister ship, it is capable of atmospheric flight, able to land on worlds to take on and disembark supplies, armor and personnel.
Designed, built, tested and brought into active service during the dark years of the War against the Strogg on Earth, the Deimos probably saw action before the invasion of Stroggos, although precisely which and how many engagements it was involved in is not known.
In order to launch the invasion of the Strogg home-world, Stroggos, the Deimos and the Phobos traversed the incalculable distances to Stroggos through a Strogg Slipgate, planted in Earth's orbit years earlier by the Strogg.
The invasion in which both the Deimos and the Phobos were to play such critical roles would not see the two vessels landing on the world, or sending the invasion force down in Drop Ships; they would instead launch their entire invasion force at the planet in small, specially designed Drop Pods.
The Pods would be held in row upon row of specially designed launch tubes, the exit hatches of which would pepper the exteriors of the port and starboard sides of both ships. The Marines and their gear would be loaded hours beforehand, while the ships were still on Earth. It is probable that the ships contained interior hangar facilities behind the launch tube arrays, for the repair of malfunctioning Pods, or reloading a second wave, or for conventional missiles It has never been specified whether the launch tubes served a secondary, missile-firing purpose, or whether spare Pods were held in reservein case of emergency evacuation.
Conventional wisdom held that, because the Strogg's planetary defense systems would detect and shoot down anything over a few meters in length, the only way to successfully transport personnel en masse to the surface of the world was to use a means of transportation too small to be detectable, allowing beach heads to be established and air defenses lowered before the Strogg could organize a response. The means to that end was to be the Drop Pods. The Pods were small and cramped by design, function holding sway over form, so just one Marine and a certain amount of equipment (alongside guidance and propulsion systems) would fit into each Pod.
During the launch of the invasion, all of the Deimos' Pods were successfully launched, although the descent would not go smoothly for all: One Marine was killed when his Pod was struck by an energy bolt fired into space from surface-based anti-air battery, and others may also have been killed by the waves of Gorgon Fighters that rose up and harassed the Pods during their descent.
However, this was just the beginning, as the planetary defense systems were online and well aware of the invasion, and were about to play an important role in it coming so close to failure. The role of the Deimos in the ground invasion snatching victory from the jaws of defeat was tactical and intelligence-based, primarily focused on distributing orders and the latest intelligence among the surviving squads and individuals in the field. Eventually, it would become more involved as the planetary defenses came down and its Air Wing was dispatched to the world below.
Following the joint launch of their entire compliments of Marines in their Drop Pods, the capital ships' Command Centers, watching for activity coming from the surface as well as keeping a close eye on the life signals and positions of every Marine, registered an unexpected and enormous Electromagnetic Pulse (E.M.P.), emanating from the vicinity of the Big Gun defense system. The Deimos' Command crew radioed the Marines and alerted them to the situation, but it was already too late: the signals of entire squads quickly began going dead in alarming numbers.
As the deteriorating ground situation was becoming apparent, and while Commanders were receiving and distributing orders and intelligence to the remaining ground forces, the two capital ships suddenly and unexpectedly became trapped in the planet's orbit, prevented from withdrawing to a safe distance by a Strogg device called the Gravity Well. When activated, it projected an enormous, powerful cone of artificially high gravity up into space, which the enormous drive engines of the Deimos weren't able to compensate for.
Thus, new orders were dispatched to sections of the Marines as they descended to the planet's surface. The orders were to destroy or otherwise disable the device creating the gravity well. Most of the Marines in receipt of the fresh orders were either killed or captured, several of them during an assault on the Well itself.
Only one Marine given the new orders, Pvt. Stepchild, one of the Deimos' own who had crash landed many miles from his Landing Zone (LZ) in an underground facility, was able to carry them to completion and free the entrapped ships, but only after undergoing much hardship. Stepchild appropriated an experimental enemy fighter during his escape from the huge subsequent explosions, safely piloting it back to his command ship - the Deimos.
At the same time Stepchild was making his way across Stroggos toward his objectives, many other surviving Marines were doing the same, watched closely by Command (in which the atmosphere must have been unbearably nervous). Numerous lone Marines and groups of survivors were killed or taken in attempting to reach and take their objectives. Those survivors following in their wake would bear witness to this, finding the fallen bodies of their friends and comrades scattered throughout the complexes and facilities they had tried to take. Many of these survivors would in turn join them.
It has never been stated exactly how many Marines the Deimos managed to recover from Stroggos during and following the first invasion. However, considering that the ship was broadcasting messages to planetside survivors on a regular basis, stating that only about 5% of the total ground force was still combat operational soon after the invasion was launched, does not bode well for any future search for survivors.
The current status of the Deimos is unknown, presumed withdrawn from the combat to wait for the reinforcement from the Second Invasion of Stroggos, continuing the operation to eliminating the entire Strogg once and for all.
- In ancient Greek culture, Deimos was the personification of terror and the twin brother to Phobos, his name translating into English as 'Dread'.
- Deimos is the name of the second Mars' two asteroid moons.
- Doom's Episode 2, The Shores of Hell, takes place on Deimos.