Hive Fleet Leviathan

Hive Fleet Leviathan is a Tyranid hive fleet, the largest recorded to have entered the galaxy, and an invasion swarm directed by the Hive Mind. It holds allegiance to no power beyond the Hive Mind itself, standing as a xenos threat to the Imperium of Man, the Aeldari, the Orks and the T’au Empire alike. First detected in 997.M41, Leviathan departed from earlier Tyranid precedent by approaching from beneath the galactic plane rather than the eastern fringe, and its arrival opened what Imperial record keeps as the Third Tyrannic War.

As with all hive fleets, Leviathan has no homeworld, crownworld or fixed territory; it exists as a migratory biomass of bio-ships, spore-born organisms and the synaptic creatures that bind them to the Hive Mind’s will. Inquisitor Fidus Kryptman’s astrotelepathic survey, remembered as the Kryptman Census, identified Leviathan’s advance as two vast tendrils separated by hundreds of light years and closing on the worlds trapped between them like a pair of jaws. Each tendril carried the Shadow in the Warp, the psychic static of the Hive Mind that severed astropathic contact and hindered Warp travel, stretching Imperial defences across the Ultima Segmentum, the Segmentum Tempestus and into the Segmentum Solar.

The tendril set on a course toward Terra was halted at Tarsis Ultra, where Ultramarines, Mortifactors, Astra Militarum regiments and a Deathwatch kill-team under Kryptman broke the swarm’s synaptic control from within. Elsewhere Kryptman ordered a galactic cordon of evacuation and Exterminatus meant to deny Leviathan biomass, a measure that slowed the fleet at grave cost in Imperial lives and led to his censure by the Inquisition. Cast out but undeterred, Kryptman later diverted a tendril into the Ork empire of Octarius by seeding a captured Genestealer brood in its path, drawing fleet and Orks into the protracted Octarius War that has continued to consume both sides.

The formation of the Great Rift severed much of Leviathan from the rest of the fleet as it turned upon Baal, homeworld of the Blood Angels Chapter; the resulting battle, fought alongside the Indomitus Crusade and complicated by the intervention of Daemonic forces under the Bloodthirster Ka’Bandha, broke the bulk of the attacking swarm. In the era that followed, Leviathan is recorded as renewing its assault through new tendrils, styled Grendyllus, Nautilon and Promethor, pressing into the Segmentum Pacificus toward the Segmentum Solar and opening what Imperial historitors term the Fourth Tyrannic War.

Leviathan’s bioforms are consistently recorded with pale, whitish carapace marked by purple hue, a colouration by which Imperial forces have learned to identify its tendrils among other hive fleets.