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Carnifex Attacks

A Carnifex of Hive Fleet Leviathan leads a swarm against the forces of the Imperium.

Hive Fleet Leviathan was the third and largest Tyranid hive fleet to invade the Milky Way Galaxy from beyond the intergalactic void. It first arrived in 997.M41 and its assault marked the start of the Third Tyrannic War for the Imperium of Man. This conflict was brought to a brief pause through the efforts of Inquisitor Lord Fidus Kryptman of the Ordo Xenos, who successfully diverted a large portion of the hive fleet into an assault upon the Ork Empire of Octarius in the Octarius System.


A Tyranid Warrior of Hive Fleet Leviathan displaying its distinct colour scheme of white skin with purple carapaces for all of its bioforms.

The crowded Greenskin cities, so teeming with life, were the source of a huge Orkoid infestation, and soon drew almost the entirety of the Leviathan into the tight cluster of star systems that comprised that Ork Empire. The plan worked, and both xenos species were soon more preoccupied with destroying each other in what became known as the Octarius War than continuing their attack on Imperial space.

Additionally, another tendril of the Leviathan was defeated by the Blood Angels Chapter and their successors among the Sanguinary Brotherhood of the Adeptus Astartes at the Battle of Baal during the early Era Indomitus, aided by an unexpected assist from the Daemonic Blood Legions of Khorne under the command of the Bloodthirster Ka'Bandha.

In the wake of these defeats and delaying actions, the Leviathan's Hive Mind altered its strategic approach and moved against the weakened Imperial defences in the more remote regions of the Segmentum Pacificus in the galactic west while Imperial forces under the command of Primarch Roboute Guilliman were preoccupied with the prosecution of the Indomitus Crusade in the Segmentum Solar and the Segmentum Ultima of the Imperium Sanctus.

This new assault, divided up between massive tendrils of the Leviathan codenamed Hive Fleet Grendyllus, Hive Fleet Nautilon and Hive Fleet Promethor, marked the onset of what Imperial historitors named the Fourth Tyrannic War.


Third Tyrannic War


Tyranid incursions into the Milky Way Galaxy after the formation of the Great Rift, ca. 999.M41; note Hive Fleet Leviathan's path from the galactic south.

The Third Tyrannic War began less than five standard years after the defeat of Hive Fleet Kraken in the Second Tyrannic War, when Inquisitor Lord Fidus Kryptman noted the tell-tale signs of yet another Tyranid invasion in 997.M41. He implemented the "Kryptman Census," burning out dozens of astropaths in the attempt to contact scores of worlds on every fringe of the Imperium. Slowly, the responses -- and lack of them -- formed a pattern, and the venerable Inquisitor was able to chart the course of the Tyranids' latest hive fleet to arrive in the Milky Way Galaxy.

Codenamed "Leviathan" by Imperial scholars, this time the Tyranids were approaching from below the galactic plane, attacking from two points spaced wide apart in the shape of a closing pair of jaws, cutting off large portions of the galaxy from Warp travel or astropathic communication. At a great cost in Human life, a combined force of Planetary Defence Force troops, two regiments of the Astra Militarum, the Ultramarines and Mortifactors Chapters of Astartes, and a Deathwatch kill-team under the command of Inquisitor Kryptman crushed the left "half" of the Leviathan on the world of Tarsis Ultra, destroying the Tyranids nearest to Terra, and reestablishing astropathic contact with the worlds between Leviathan's jaws. The Imperium had won its first victory.

Yet Leviathan continued to carve its bloody path through the Imperium. Perhaps Leviathan's main gain was the vital Forge World of Gryphonne IV, home of the Legio Gryphonicus Titan Legion. Kryptman knew he had to slow down the Hive Fleet's advance to buy time for the Imperial Navy's Battlefleets Solar and Tempestus to muster. With grim finality, he ordered a cordon to be established. Every world within was to be evacuated and undergo immediate Exterminatus wherever possible, thus causing the Tyranids to expend their forces for little gain, the Exterminatus denying them valuable biomass to replenish themselves. With one stark, callous decision, the Inquisitor had inflicted the Imperium's worst act of genocide upon on its own since the Horus Heresy. Kryptman was denounced as a radical and a traitor; when migrating Orks claimed a score of former Human worlds, he was stripped of his title and cast from the Inquisition by his brethren.


Hive Fleet Leviathan invaded the galaxy from below the galactic plane, taking the Milky Way's defenders completely by surprise.

Yet Kryptman still had loyal allies within the Deathwatch, and incepted a plan to halt Leviathan without the loss of further Human life. When a Genestealer-infested space hulk drifted from the Warp, members of the Deathwatch loyal to Kryptman captured a brood in stasis. Using the brood of captured live Genestealers, the Inquisitor engineered a Tyranid invasion within the Ork-held Octarius System, very close to Leviathan's advance. The crowded Ork cities, so teeming with life, were the source of a huge Orkish infestation, and soon drew the entirety of Leviathan into the tight cluster of Ork star systems known as the Ork Empire of Octarius. The plan worked, and both races are now thoroughly involved with destroying each other in what has become known as the Octarius War.

One thing is certain: each race thrives on war, and there remains the possibility that if the Tyranids emerge victorious, the Imperium shall have to face a threat far greater than before, as in a victory, unlike other races, Tyranids effectively lose no military strength or resources, their casualties and still living warrior strains reabsorbed by invading Hive Ships along with the remains of the conquered worlds. Thus every victory has no repercussions, only benefits.

The conflict of the Octarius War also means that the Tyranids will assimilate vast quantities of the strong, survivable, highly adapatable Orkoid DNA that makes the Greenskins such successful survivors and tenacious opponents and incorporate it into their own bio-constructs. Indeed, worlds on the edge of the conflict have begun to record captures of Tyranid assault organisms that are now larger than ever before. The implications of Kryptman's manipulation of this alien threat are too horrible to contemplate.

Not long after Hive Fleet Leviathan first assaulted the the worlds of Humanity, a shadowy council within the Imperium called the Strategic Collective has been analyzing all details of the Tyranid invasions, and have drawn a conclusion as stark as it is terrifying: the fleets faced by the Imperium to date are but parts of a far greater whole, and this whole will be arriving at the Imperium's borders within less than a Terran century. They estimate that mobilisation levels will need to be increased by a minimum of 500% -- effectively including every able-bodied man, woman and child on every world in Segmentums Solar, Obscurus and Tempestus -- to have even a hope of stopping the Tyranids...

Fourth Tyrannic War

The Fourth Tyrannic War began in the Era Indomitus, when the largest mass of Hive Fleet Leviathan yet encountered attacked the Western Reaches of the Segmentum Pacificus, seeking to strike at a relatively undefended region of the galaxy while the defenders of the Imperium were otherwise engaged with the forces of Chaos emanating out of the Great Rift.

The great Tyranid assault began with the coordinated attack from above and below the galactic plane by three new tendrils of the Leviathan dubbed Hive Fleet Nautilon, Hive Fleet Promethor, and Hive Fleet Grendyllus, respectively, by the Imperium. The two tendrils were moving in parallel towards their ultimate goal of Terra in the Segmentum Solar, and with the Imperium distracted by the ongoing demands of the Indomitus Crusade few Human forces initially were available to stand against it.

Hive Fleet Appearance

The bioforms of Hive Fleet Leviathan all bear a distinct colour scheme of white skin with purple carapaces, and usually red weapon biomorphs.


  • Codex: Orks (4th Edition), p. 29
  • Codex: Tyranids (5th Edition), pp. 28-31, 59, 66
  • Codex: Tyranids (8th Edition), pg. 25
  • Warhammer 40,000: Leviathan - Rulebook (10th Edition), pp. 230-233, 238-243, 246-255
  • Leviathan (Novel) by Darius Hinks, Ch. 1