The Space Marines of the Adeptus Astartes are the mightiest warriors in the Imperium and their fury in battle is legendary. Few can stand against the might of a Space Marine Chapter and the foes of Mankind tremble at their name. But there are alien races whose evil is beyond human understanding and beings that exist outside the realm of realspace that seek to plunge Humanity into the realm of Chaos. To face such foes demands warriors whose hearts and souls are trained to withstand extremes of pain and terror, whose faith in the Emperor is as unwavering as it is strong. Since the dawn of the Imperium specially trained Space Marines have fought these foes and defeated them. They are the Deathwatch.

The Deathwatch

On uncounted battlefields, the servants of the Emperor must wage war against the vileness of alien creatures. Often the first, last and only line of defence against these abominations are mysterious figures in black powered armour who fight the aliens with preternatural skill and dedication. With the battle over, these figures vanish as quickly as they arrived, leaving no trace of the creatures they fought or that they were even there at all. These men are the Imperium's highly trained alien fighters. They are the Deathwatch.

The Deathwatch forms the Chamber Militant of the Ordo Xenos, the branch of the Inquisition tasked with the study, containment and, in most cases, extermination of alien races. However, it is not a single unified Chapter in the same way as the Grey Knights of the Ordo Malleus. The Space Marines of the Deathwatch are drawn from many different Chapters, all of which have sworn sacred oaths to maintain specially trained alien fighters and stand ready to deploy them at a moment's notice. These warriors are drawn together as and when needed to combat alien menace whenever and wherever it rears its ugly head.

From the furthest corners of the galaxy to the very heart of the Segmentum Solar, there exist alien races that threaten the continued existence of Humanity. Every Space Marine Chapter and Imperial Guard regiment stands ready to fight these races, but the Deathwatch has been specially trained to fight aliens since its inception, thousands of years ago. Many such alien races, such as the C'tan and Necrontyr have lain dormant for thousands or even millions of years and the Deathwatch stand sentinel over their worlds, ready to fight should they awake once more. More dangerous than the most violent of Orks, these races were ancient before humans crawled from the oceans and their evil is beyond measure.

To be Unclean That is the Mark of the Xenos
To be Impure That is the Mark of the Xenos
To be Abhorred That is the Mark of the Xenos
To be Reviled That is the Mark of the Xenos
To be Hunted That is the Mark of the Xenos
To be Purged That is the fate of the Xenos
To be Cleansed For that is the fate of all Xenos

Extract from the Third Book of Indoctrinations.

To guard against the return of these ancient alien races, lonely fortresses orbit desolate worlds on the edge of the galaxy where Deathwatch Space Marines maintain a constant vigil. In addition to this, secret bases are scattered throughout the Imperium, providing staging posts from where the Deathwatch can launch their missions. The Chapters from which the Deathwatch draws its members are constantly ready to despatch their alien fighters if called upon by a member of the Ordo Xenos. The warriors who have been given the honour of becoming a member of the Deathwatch ritually repaint their armour in the black of the Deathwatch, leaving a single shoulder plate bare to signify their Chapter of origin. A Space Marine's armour is never completely obscured by the Deathwatch colours as to do so would dishonour the armour's spirit and no warrior would be willing to run such a risk. Each warrior may also bear the Icon of the Deathwatch on his other shoulder plate and it is a great honour to be chosen. Once in the employ of the Deathwatch, there is no set length of service and its members will remain together for as long as its commander deems necessary. Each Space Marine can serve for a discreet period of time or a particular mission, which, in itself, may take many years. With the completion of their service, the Space Marines are free to return to their Chapter, their oaths of loyalty fulfiled.

Do not ask. Why kill the alien? rather, ask. Why not?

Battle Brother Artemis

As well as the destruction of aliens, the Deathwatch are also charged with the recovery and study of alien artefacts and technology. Though distasteful in the extreme, members of the Inquisition are forced to study the heretical artefacts of the foes they must fight, and there are none more qualified to retrieve such items than the Deathwatch. Occasionally it becomes necessary to use the technology of alien races and, though such an undertaking is never entered into lightly, its use against aliens themselves is a pleasing irony. The Adeptus Mechanicus is always eager to profit from the Deathwatch's victories and the C'tan phase sword employed by the Callidus temple of assassins, was recovered by members of the Deathwatch from a long-dead Necrontyr world.

In battle, each team normally comes under the authority of an Ordo Xenos Inquisitor, but, in some exceptional cases, a Deathwatch Captain or Librarian may assume command if circumstances dictate. Their authority is absolute and none dare question their word. The commander of a Deathwatch detachment may freely requisition forces and equipment without a word of complaint being raised against him. The Deathwatch have access to the very best equipment, both Imperial and alien, and are trained to the highest standards.

He who allows the alien to live. shares its crime of existence.

Inquisitor Apollyon

There are many ways an Ordo Xenos kill-team can see action alongside regular Imperial forces. It may be that the team has uncovered an alien threat too great for it to deal with alone and needs the backup of a larger, more conventional force. Such was the case when a kill-team under the command of Inquisitor Reynaard discovered an alien worshipping cult on the world of Mandall IV. It was believed that the cult was localised to a particular district of the capital city, but when righteous retribution descended upon the blasphemers, the entire population of the city turned upon the kill-team. Reynaard and the Space Marines barely managed to escape with their lives and later returned at the head of over half a million soldiers. To ensure the destruction of the cult, Reynaard's forces laid waste to the city, leaving no trace that it had ever existed and killed every living creature within its walls.

Situations may also arise where an army of the Imperium has encountered a foe it is ill-equipped to fight and the Ordo Xenos dispatches a kill-team to provide support or purge the battlefield of alien contamination.

The ravages of the K'nib in the Donorian Sector was halted by a Deathwatch kill-team commanded by Battle Brother Artemis himself following a request for aid from the colonel of the Kaslon Imperial Guard regiment. Artemis slew the Alcayde of the K'nib on Assumptus V and ended their incursions into Imperial space (though official records credit the Kaslon regiment with this victory). However it comes about, the support of an Ordo Xenos kill-team is always welcomed by Imperial commanders facing an alien threat.