The Kappa Mortis Incident was a brief Imperial military campaign in which a detachment from the Ultramarines Space Marine Chapter sought to recover a downed Imperial shuttlecraft containing captured T'au technology. As the Imperium had only recently encountered this new and unusually technologically advanced xenos species, the Inquisitors of the Ordo Xenos and the Magi of the Adeptus Mechanicus were eager to get their Mechadendrites on T'au wargear so that they could plumb the depths of its heretical secrets and fashion appropriate Imperial countermeasures.
The recovery mission proved successful, though the Ultramarines recovered only a single helmet taken from a T'au XV15 Stealthsuit. However, the T'au feared that this in itself would prove detrimental to the Fire Caste's tactical surprise over the Imperials, and so the Earth Caste moved to rush the XV25 Stealthsuit into deployment. This was done to get a new T'au Stealthsuit into combat that the Imperial military had not yet analysed, even though the XV25 was less advanced than the harder-to-produce XV22 Stealthsuit that was still at the prototype stage.
On the far-flung world of Kappa Mortis, the Damocles Gulf Crusade had ground to a halt. The Imperium of Man had made a major incursion into the newly discovered T'au Empire in the Ultima Segmentum, but was forced to pull its forces out of T'au space in response to the far greater threat posed by the Tyranid Hive Fleet Behemoth, which had begun devouring entire sectors on the nearby Eastern Rim. Kappa Mortis had been evacuated by the Imperial military, and the T'au, rapidly re-consolidating their grip on those worlds captured by the Imperium during the first stages of the Damocles Gulf Crusade, moved to reclaim it.
One of the last Imperial vessels to leave Kappa Mortis was an Aquila Lander, a messenger shuttlecraft bearing captured T'au technology bound for the laboratories of the Ordo Xenos. But before it could reach orbit, the shuttle was engaged by T'au fighters and was shot down. The shuttle crashed amongst the buildings of the now deserted Imperial outpost Theta Seven, its pilot activating his emergency beacon as he attempted to bring his ship in intact.
Although the Aquila Lander was wrecked, its homing beacon survived. During its brief battle with the T'au interceptors, the Aquila sustained serious damage to its plasma reactor system. Although the pilot managed to eject one reactor core, the second failed to release and went down with the shuttle. Both of these cores were unstable and gave off dangerous radiation. This would add a extra layer of danger later on to both forces involved in the incident.
Captain Agemman of the Ultramarines, en route to the Realm of Ultramar in response to the threat of the Tyranid Hive Fleet Behemoth, received the shuttlecraft's distress message. He realised instantly that the captured T'au technology aboard the lander might prove valuable to the Imperium, but he could spare few warriors from the coming battles against the Great Devourer. He led a small detachment to investigate, while the remainder of his force hurried on to face the Tyranids within Ultramar.
The battle that followed was short but extremely bloody. The T'au ambushed Agemman's forces as he directed the search of the crash site. The Utlramarines repulsed the T'au attack, though Agemann was wounded during the action. Crucially, Agemman's force recovered a single item of T'au technology, the helmet from an XV15 Stealthsuit. This forced the T'au Earth Caste to accelerate the development of a new Stealthsuit as a result, rushing the single-weapon XV25 Stealthsuit into service ahead of the harder-to-produce but more advanced XV22 Stealthsuit they had hoped to introduce en masse to the T'au Fire Caste.
Imperial Forces Order of Battle
The Ultramarines selected to take part in the operation were drawn from the Chapter's 2nd Company, which consists of a balanced mix of the various squads available to a Space Marine commander. Agemman had no time to gather intelligence on his foe and could spare precious few warriors for this mission. Therefore, he hand-picked a small but well-rounded force, one capable of performing a fast search-and-destroy operation before withdrawing once more.
Force Agemman was based around a core of fifteen Tactical Marines, organised into a full strength, ten-man squad and a smaller, "Combat Squad" of five Astartes. These were supported by a Scout Marine sniper squad, who were tasked with performing an initial sweep of the crash site before spreading out to act as sentries once the search of the wreckage was underway. Captain Agemman, accompanied by his Command Squad, directed the search operation, whilst Dreadnought Ferrous, Assault Squad Venio, and a Predator acted as a mobile reserve, holding station nearby to counter any T'au move made against this search force.
Agemann's plan during the Kappa Mortis Incident followed tried and tested methods laid down millennia ago in the Codex Astartes -- the great book of tactics, organisation and collected military wisdom penned by the Ultramarines Primarch Roboute Guilliman. He ordered his core force, centred on two Tactical Squads, to perform the search of the crash site. Meanwhile, the Scouts would seek high ground from which to maintain a watch on the surrounding area, and to engage any enemy that approached, pinning them while the mobile reserve element of the force deployed to block their assault.
T'au Forces Order of Battle
Facing Force Agemman was a small detachment of T'au Fire Caste warriors, drawn from the race's home Sept of T'au. Their Commander was a newly promoted Shas'el whose name translated into Low Gothic as Nightwind. His orders were simple -- recover the items stolen by the Humans or, at the very least, deny the warlike Imperium its prize at all costs. Nightwind's compact force, led by Nightwind himself, was perfectly placed to intercept the enemy at the site of the shuttle crash.
Detachment Nightwind comprised a twelve-warrior team of Devilfish-mounted Fire Warriors, with a second six-warrior-strong unit in support. Additional mobile firepower was provided by a Hammerhead gunship and three Piranha light skimmers. The force was led by Commander Nightwind and his adjutant, Shas'Vre Ka'eldi. Lastly, an XV25 Stealthsuit team led by Shas'Vre Kai'leath provided the detachment's reconnaissance force. It was they who located the crash site first and directed the rest of Detachment Nightwind to their objective. During the confrontation, Commander Nightwing made use of a sophisticated sensor array issued by the Earth Caste and built into his Battlesuit's "head" to help him locate the stolen T'au technology.
Commander Nightwind's orders were dictated by the disposition of his forces at the time the crashed Imperial shuttle was located. His Hunter Cadre was scattered throughout the region, his Stealth Teams, equipped with the new XV25 Stealthsuits, ranged far and wide. When Stealth Team Kai'leath reported the crash site found, Nightwind ordered them to engage the Imperials and to engage targets of opportunity whilst his forces raced to the scene. Nightwind knew that he was asking Kai'leath's warriors to tackle a larger and more powerful foe, but he could not risk the enemy escaping. Such is the way of the Greater Good.
- White Dwarf 321 (UK), "The Kappa Mortis Incident", pp. 76-81