The Hydra Attacks

The Hydra Attacks is the name of the Imperial defensive campaign conducted by the Grey Orphans Space Marine Chapter against a ravaging splinter-fleet of the Tyranids' Hive Fleet Hydra.

Background
Simultaneously with the struggle against the Forces of Chaos, in the Segmentum Tempestus, another threat was revealed: the extra-galactic predators known as Tyranids. A tentacle of the Hydra bio-flotilla threatened the Tarchon System. To address the new threat, all available companies and the newly formed Tarchonian Astra Militarum Regiments were deployed. The defences were deployed on Tarchon and its moons to counteract the alien monstrosities, the Planetary Defense Forces resisted the first waves, but the overwhelming number of the Tyranids forced the gray orphans and imperial soldiers to retreat. On Tarchon Primus the 2nd and the 7th Companies saw the number of their own troops reduced in an alarming way.

On Tarchon Secundus the 5th Company and several companies of the Tarchoniana Guard were completely exterminated leaving the Tyranid forces to consume Tarchon's moon. Only the timely intervention of a contingent from the ongoing Indomitus Crusade which brought newly revealed Primaris Space Marines to bolster the Chapter's sorely depleted ranks, were they able to save the destiny of the sorely depleted Chapter and the entire system.