When the first Imperial
forces finally reached the distant world of Tyran Primus in response to its pleas for aid,
they were confronted by an enigma. Tyran had been an oceanic world, yet now its shimmering seas were
simply gone, along with every plant, every animal, every bacteria. A verdant world had stripped bare,
indistinguishable from the lifeless rocks that are common across the galaxy.
Of the research outpost present in the world, only ruins remained and a single data codex,
found at the bottom of a Mechanicus borehole that had extended miles into the planetary crust.
This codex, preserved at terrible cost, would be the first written record of the
vast alien intelligence that would take the name of Tyran as its own.
Many centuries and thousands of consumed worlds later, the breadth of reports, intelligence and
reconnaissance concerning this new threat has broadened mankind’s knowledge a thousand fold.
Yet when mobilized against the vast swarms of the Tyranids, the Imperium still confronts an enigma.
Hive Fleet Leviathan is the ultimate expression of mankind’s ignorance regarding the Tyranids.
Imperial officials cannot even agree on where it begins or ends;
what constitutes the main force and what is merely a splinter fleet or lesser tendril.
Like the Tyranids themselves, Leviathan is simply too big for human minds to comprehend.
Similar in structure to the two other major hive fleets encountered by the Imperium;
Behemoth and Kraken, Leviathan is an immense armada of bioengineered predators.
From colossal hive ships the size of star forts, to the endless masses of
creatures gestating within them, it is a complete spaceborne ecosystem.
As it descends upon verdant worlds, it consumes every trace of biological matter, collecting them
into great digestive pools to acquire their base nutrients and genetic material. Leviathan however,
eclipses both Behemoth and Kraken by an order of magnitude in both size and sophistication.
By even the most conservative estimates, Leviathan
is the greatest concentration of organic life in the galaxy.
Its numbers eclipse the total human population, or even that of the Orks by a phenomenal margin.
Where previous Hive Fleets entered the galaxy from the Eastern Fringe, Leviathan approached
from beneath the galactic plane in a maneuver startlingly similar to the hunting patterns
followed by oceanic predators. Consequently the hive fleet has emerged across a wide section of
the galaxy, consuming worlds thousands of light years apart. This unique approach has impeded the
Imperial response to Leviathan, with human minds predisposed towards two-dimensional thinking.
Yet Leviathan also appears to be the most evolutionarily advanced Hive Fleet yet
encountered. It is generally understood that the Tyranids utilize sophisticated methods to
facilitate the transfer of genetic material across species, incorporating the beneficial traits from
trillions of different life forms into their own. With the Leviathan however, the outcome
of this process is the most pronounced. It has been speculated it possesses the genetic material
acquired not only from its own advance across the galaxy, but also from other Hive Fleets.
If this is accurate, then Leviathan is the result of every adaptation and evolution
made by every Hive Fleet within the galaxy. Imperial strategy when facing the Behemoth
and Kraken Hive Fleets was to target “synapse creatures”, special bioforms within a Tyranid
swarm in which the link to the greater Hive Mind is strongest. Through a form of telepathy,
Synapse creatures relay the directives of the hive mind to every organism. Without synapse
creatures to project the hive mind, lesser Tyranid bioforms revert to crude, animalistic behaviors.
Leviathan is still vulnerable to this tactic, but the synaptic network present
across the Hive Fleet is more powerful and more resilient than anything ever before encountered.
Imperial reports concerning Leviathan are full of accounts of synapse creatures that
have been severely wounded or even blown apart by explosives that nevertheless
maintained a connection with the Hive Mind, and continue to direct other tyranid bioforms.
Even mortally wounded Tyranids, their limbs shattered and bodies crushed,
have nevertheless arisen as if from the dead, compelled to fight on by the Hive Mind. Whether
this is due entirely to the superior strength of Leviathan’s synapse connection, increased
resilience in the physical makeup of its swarms, or some combination of the two, remains unknown.
Even more concerning are Levithan’s Swarmlords, Apex Warriors, and Hive Tyrants.
Though merely tools through which the Hive Mind exerts its control over the rest of the host, some
have shown a great degree of cunning and tactical brilliance when set against specific elements of
the Imperium’s defenses. It is theorized that these have been purposely crafted by the Hive
Fleet as direct counters to Imperial formations, strategies, or even individual leaders. More than
any other Hive Fleet, Leviathan appears to act with singular purpose, and extreme precision.
Leviathan has also become known as the Hive Fleet in which several “new” Tyranid strains were first
encountered. Several of these appear to be a response to the Imperium’s own “Age of Witches”,
in which the number and raw power of psykers dramatically increased across the galaxy.
The Hive Mind always possessed a unique ability to nullify psychic power, usually referred to as the
“Shadow in the Warp”, but this has increasingly been imbued directly into Tyranid bioforms,
the “Neurotyrant” in particular. Even a highly trained Astartes librarian might find their
psychic abilities rendered inert by the mere presence of a Neurotyrant. The Hive Mind has
seemingly even found a new method of utilizing the biomass of consumed Psykers, converting their
very essence into a grotesque form of ammunition - psychocorrosive ash spewed out by “Psychophages”.
These new life forms in particular seem to play into Leviathan’s greater strategy.
Its approach from beneath the galactic plane has had the added benefit of spreading the
Shadow in the Warp across a far wider area and the presence of Neurotyrants
and Psychophages gives credibility to the idea that the Hive mind considers
psychic powers a particular threat to its advance across the galaxy.
Hive Fleet Leviathan is first recognized to have entered the galaxy in the year 997 of the 41st
millennium, roughly two and a half centuries after Behemoth and only 5 years after Kraken.
Its tendrils represented a great pincer, within which thousands of star systems were
cut off from the Astronomicon and warp travel made untenable. Of greatest alarm however,
was that one tendril within this pincer seemed to be advancing directly towards Terra.
A combined force of Astra Militarum Regiments, Astartes of the Ultramarines and Mortifactors
Chapters and Deathwatch Kill-teams successfully eradicated the main strength of one of these
tendrils, breaking the pincer on the world of Tarsis Ultra. The threat to Terra was reduced, but
the main strength of Leviathan continued to churn through the Imperium elsewhere in the galaxy.
With few options, the Imperium has increasingly relied on exterminatus
measures to prevent Leviathan from acquiring new biomass.
This has resulted in the greatest genocide of Imperial Citizens since the Horus Heresy,
but is nothing more than a stopgap measure. More desperate strategies have involved luring
the Tyranids into Ork infested space, though even the Ork Empire of Octarius appears to have
largely fallen to Leviathan, swelling its hive ships with an enormous quantity of biomatter.
It was on and above the world Baal, Chapter Homeworld of the Blood Angels that Leviathan
suffered its most monumental defeat. But the Imperium’s victory came at a tremendous price.
Faced with the largest single concentration of Leviathan organisms,
or any Tyranid Hive Fleet ever observed, the area of space surrounding Baal,
a region known as the Red Scar, was subjected to widespread exterminatus measures.
Hit and run attacks throughout the region against the numerically superior Tyranid
force crippled Astartes' void warfare assets and Imperial Navy battlegroups.
When the fighting reached Baal itself, the Sanguinary Brotherhood,
a near-legion sized Astartes force consisting of the Blood Angels and their brother chapters,
was subjected to horrific carnage. As many as eight Space Marine chapters
were completely annihilated, and as many more were left dangerously understrength.
The leadership of Commander Dante, Chapter Master of the Blood Angels, and the timely arrival of the
resurrected Primarch Roboute Guilliman earned much of the credit for the victory, though the
cost would have been far higher were it not for the intervention of the Bloodthirster Ka’Bandha.
Though the motives of the servants of the Blood God in saving their hated rivals were
likely the result of ancient grudges, for both the Imperium and the dark powers of Chaos to
even briefly confront a mutual foe together, underscores the sheer power of Leviathan.
For a time it was judged that the victory at Baal had devastated Leviathan, but the enormous
tendrils of Tyranid bioforms that ripped through the Red Scar, were but one amongst many in the
greater hive fleet. More tendrils have already appeared elsewhere in the galaxy, with another
enormous mass speculated to be encroaching on the Western Reaches of Segmentum Pacificus.
As before, the projected routes of this new invasion lead directly to Holy Terra.
On the Imperial throneworld itself, a secret research group has been established within
the immense Adminstrarum Complex. Known as the Strategic Collective, it has brought together
the savants of the Inquisition, whose minds have been augmented to perform inhuman calculations,
Magos Biologis of the Adeptus Mechanicus, whose knowledge of genecraft is unmatched,
and representatives of every other Imperial institution whose expertise might be useful in
understanding and destroying the Tyranid threat. Among the many theories posited by this assembly,
is one that if true, reduces the chances of an Imperial victory, to the slimmest of margins.
Some within the Strategic Collective speculate that Hive Fleet Behemoth and Hive Fleet Kraken may
not have been genuine attempts by the Hive Mind to annihilate the Imperium, or any other major power
in the galaxy. They were probing attacks, tests. Behemoth was a crude battering ram,
designed to determine how galactic civilizations would respond while Kraken was a systematic effort
employed to keep any potential resistance unbalanced and divided. Leviathan represents
the first real effort by the Hive Mind, the first true expression of the Tyranid race.
The enigma of Leviathan and the Tyranid Hive Mind is unlikely to be solved by the
Strategic Collective. There is only one truth the Imperium must contend with, one irrefutable fact
at the heart of the Tyranid race: they are no longer a distant concern, they are here.