The carapace of every single Tyranid organism spawned by Hive Fleet Tiamet -- like this Tyranid Warrior -- is made of a unique chitin composite that provides excellent protection against extreme bursts of directed energy and kinetic force.
Hive Fleet Tiamet is a minor Tyranid hive fleet that first entered the Milky Way Galaxy no later than the 35th Millennium in what may have been a probe to survey the Hive Mind's next major target ahead of the main Tyranid fleets' arrival in the 41st Millennium.
Named after the Tiamet System in which it was first encountered, Hive Fleet Tiamet is a unique phenomenon: a Tyranid incursion fleet which has claimed a cluster of planets without entirely stripping them of biomass.
Its primary base of operations in the system is the Jungle World of Ziaphoria, the surface of which it has begun to tyrannoform into some type of biomechanical psychic resonator whose purpose remains unknown and worrisome to the Ordo Xenos of the Inquisition.
The hive fleet continues to guard its conquered territory with single-minded ferocity.
Only the Deathwatch Space Marines of the nearby Watch Fortress Haltmoat -- and Inquisitor Fidus Kryptman, who came out of his long exile to join them -- had any inkling of the threat posed by the immense psychic resonator of Tiamet.
The theories they discussed long into the night were so wild, and the other threats facing the Imperium in the Era Indomitus so dire, that they were given little credence by the wider Inquisition.
History
First Contact
Tiamet was the name given to a large, double binary star system on the Eastern Fringe discovered in the 35th Millennium by an Adeptus Mechanicus Explorator fleet hailing from the Forge World of Triplex Phall.
The Tiamet System was remarkable in that it contained no less than seven large life-sustaining worlds and a host of lesser planetoids. The Explorators discovered to their cost that every biosphere in the system was a Death World of the most voracious kind.
Whether the prevailing climate was jungle, ice or desert, or even airless rocks, a host of dangerous life forms swarmed, multiplied and warred on each other with an uncanny intelligence which united them against Man's intrusion with deadly results.
Xenologists eventually determined that the life all over the system shared a common genetic ancestry and had developed various ways to get from world to world to seed new territory.
Realising their own craft would be contaminated from entering the system by now, the Explorators quarantined themselves in the Tiamet System. They were to survive and report for another hundred and sixty-two solar hours before succumbing to the lethal denizens of that fecund realm.
Tiamet was systematically fusion bombed on several occasions by Imperial vessels but life was never extinguished there; it now lies within the area swept over by Hive Fleet Kraken and as such its fate is unknown.
Most theories about Hive Fleet Tiamet place it as an implant-probe, believing that some kind of Tyranid genetic seed, possibly molecular-coded DNA, is responsible.
By some means (perhaps cosmic debris or solar winds) the Tyranid seed was introduced to the system and spread of its own accord to form its own rudimentary Hive Mind and predatory ecosystem.
Horror on Ziaphoria
The Tiamet System then went largely undisturbed for the next few thousand standard years. It was only when a small force of Aeldari Rangers from Craftworld Iyanden happened upon the isolated system that a troubling secret was discovered.
Upon nearing the largest planet in the system -- the Jungle World of Ziaphoria -- the Rangers discovered a continent-spanning organic construct, a conical super-structure formed of chitin and soft, encephalic flesh that thrummed with immense psychic energy.
The Shadow in the Warp was horrifically strong here, and several of the Asuryani went into convulsions upon nearing the super-structure, their minds sent into shock by the sheer force of Hive Fleet Tiamet's nullifying aura.
What purpose this bizarre device serves is yet unknown, but for the Hive Mind to devote an entire fleet to its protection is a worrying portent. Ordo Xenos Inquisitors have theorised it may be a powerful psychic beacon, guiding yet more Tyranid hive fleets into the galaxy.
In recent years, sightings of questing Tiamet tendrils have become worryingly common, as the hive fleet seeks fresh yields of biomass with which to finish its creation. For instance, in 998.M41, remnants of Hive Fleet Tiamet were confirmed to be in the Segmentum Obscurus, although there is no information of how they got from the Eastern Fringe to there.
These hosts have proven extremely difficult to kill, shrugging off volumes of fire that should have seen them utterly obliterated.
Choir of the Void
Upon the world of Heinrich's March, worshippers of the Dark Gods work their tortured slaves to death as they attempt to erect a monolithic ziggurat in honour of their foul patrons.
In time, a new and hidden cult propagated amidst the persecuted masses: the Choir of the Void. Its leader, the blind prophet known only as "the Conduit," preached that a saviour race from beyond the stars awaited them in a far-off place, a paradise planet where they would find salvation.
In a great uprising, millions of Human slaves overwhelmed their dark masters and commandeered several dozen cargo hulks. This armada of the faithful made for the nearby Tiamet System, guided by the visions of the Conduit.
In truth, Ziaphoria, the repugnant and anomalous Jungle World claimed by Hive Fleet Tiamet in the system, had become the site of a disturbing new development in the curse of tyrannoforming, the hyper-accelerated biological process that is used to overcome and devour the prey worlds of the Hive Mind.
There the conquering hive fleet constructed vast psychic resonators of fleshy, encephalitic material -- some the size of mountains, some large enough to cover entire continents.
The vast pilgrimage of Genestealer Cultists that had set out from the nearby planet of Heinrich's March eventually landed upon Ziaphoria's pulsating crust.
Those who touched the corrupted earth with their bare flesh were instantly brought in thrall to the Hive Mind of Tiamet -- and convinced their brethren to go back into space as missionaries, carrying the Creed of Tiamet to as many Imperial worlds as possible.
They were the first of dozens of interstellar pilgrimages that sought out Ziaphoria, and in doing so, added to its power.
The Tyranids of Hive Fleet Tiamet defended the planet so ferociously it was declared Quarantine Extremis and abandoned entirely by the Imperium.
A Nightmare Unearthed
As time passed, more and more reports of missing Imperial starships and lost fleets in the region drifted in to the Deathwatch's watch fortress Haltmoat. The common denominator in each of these cases was that the vessels were last reported in the vicinity of the Tiamet System, far from safe haven.
Watch Commander Vilnus ordered an immediate survey of the area.
Kill Team Gjunheim departed from Haltmoat to investigate the reports of missing trade fleets near the Tiamet System. The Deathwatch drifted in-system unnoticed, and landed upon Ziaphoria.
There, they discovered the biomechanical xenos super-structure that covered the planet's largest continent. When this vast device pulsed, sending a tsunami of psychic energy rolling across the planet, the kill-team's Librarian suffered a catastrophic cranial rupture.
His screams alerted nearby Tyranids, and soon the remaining battle-brothers were surrounded by swarming xenos. Before he and his remaining battle-brothers were torn apart, Watch Sergeant Gjunheim managed to send one final vox transmission to the team's orbiting Corvus Blackstar, warning of the nightmare his warriors had uncovered.
Kryptman Returns
In the wake of these events, watch fortress Haltmoat received an unexpected guest -- the infamous exiled Inquisitor Fidus Kryptman. Watch Commander Vilnus agreed to an audience with the outcast, who has his own grim theories regarding the mysterious Hive Fleet Tiamet.
Together, the two began to formulate a plan that will see whatever the Tyranids are creating on Ziaphoria utterly obliterated.
Ymgarl Genestealers
It is believed that the variant Ymgarl Genestealers were introduced to the moons of Ymgarl, where they were first encountered by the Imperium, from the Tyranid organisms originally present in the Tiamet System and discovered by the Explorators in the 35th Millennium.
They were carried to the moons of Ymgarl within the very vessels that had been sent to destroy the voracious lifeforms present in the Tiamet System.
Traits
The carapace of every single organism spawned by Hive Fleet Tiamet is made of a unique chitin composite that provides excellent protection against extreme bursts of directed energy and kinetic force. The hive fleet's organisms and bio-ships were heavily protected by this living battle-plate.
Built to protect as much as devour, Tiamet's swarms fight in dense clutches, grinding their way forward through hails of enemy fire, their diamond-hard exoskeletons forming a formidable living shield.
All Hive Fleet Tiamet bioforms possess grey and white carapaces.
Sources
- Codex: Tyranids (4th Edition), pg. 24
- Codex: Tyranids (8th Edition), pg. 38
- Codex: Genestealer Cults (8th Edition), pg. 39
- Warhammer 40,000 Rulebook (5th Edition), pg. 166