Drycho Nautocracy Xenocide

The Drycho Nautocraxy Xenocide was an Imperial xenocidal purgation campaign fought by detachments of the Jonmarines Space Marine Chapter against the Gras'Vak, a minor xenos species. This conflict was a part of the much larger Reconstruction Wars in the Chapter's history.

History
Beleaguered Imperial settlers on the world of Drychos were relieved to bear witness to the arrival of the Jonmarines’ Fifth and Tenth companies, Taskforce Haarnvust, in retaliation to their reports that many of the settlements established had been eradicated by partially amphibious, humanoid, fish-like beings known as the Drycho. Using both their superhuman physiology and reconnaissance submersibles built by the Imperial settlers, Captain Haarnvust, Chaplain Mihos and Librarian Civares, alongside a number of scout squads, are able to follow the Drycho back to their lairs, while Captain Al' Khephit and his Fifth move to protect the Imperial civilians from further attacks.

After a few months of stalking the Drycho, in which several thousand of the xenos are hunted down, Al'Khephit receives a message written in a crude approximation of High Gothic demanding a “summon to battle” from the Drycho’s “Nautocrat”, who claims that the Jonmarines’ defence of the Imperial settlers on Drychus was a further act of war against their species. The Jonmarines accept this orderly declaration of war, and soon assemble forces at the Gyrach Basin, a coral reef at the bottom of the shallow Lythman Sea, which comprises 75% of Drychus’ surface. Here, the Drycho show themselves as not only technologically advanced, but ordered and disciplined, honourable even, as the Nautocrat challenges Daviaan to single, honorary, combat in full display of both sides’ troops. With the Nautocrat’s death, however, the battle commences, and the Gyrach Basin soon becomes choked with Drycho blood and viscera, their weapons unable to breach the Jonmarines’ ceramite plate, while their light, loose-fitting, armour fails to protect against bolter fire, even that slowed in the subaqueous conflict. With a majority of the Drycho’s number eradicated, Drychus is declared safe for human habitation, but not before the Jonmarines teach the settlers how to deal with the Drycho threat, should the need arise once more.