Hive Fleet Tiamet

Hive Fleet Tiamet is a small Tyranid Hive Fleet first encountered in M35, considerably sooner than the first major Hive Fleet, Behemoth.

Discovery of Tiamat

Hive Fleet Tiamat was first encountered around the Tiamat system, on the eastern side of Ultima Segmentum. Considering this region is quite unremarkable for any of the major powers of the galaxy beforehand, the Imperium made first contact with it through a small exploration fleet, technically making this the Imperium's first contact with a Tyranid Hive Fleet. They didn't consider the presence of the tyranids in the worlds around Tiamet something threatening, believing they were just the natural fauna of a Death World. Because the Imperium had other things to worry about, and because the area had no real value, it was left undisturbed (they did throw a symbolic bombardment of the place once, though, to no real effect).

It wouldn't be until a fleet of Eldar explorers when someone recognize the tyranids for what they were. However, what they saw there was extremely disconcerting.

Behaviour of Tiamat

Regular tyranids follow a nomadic lifestyle, travelling though the galaxy and devouring whatever planet or biomass source they can find, usually following the psykic beacons activated by the multiple genestealer cults spreaded throughout the galaxy, leaving wherever they go bereft of life. Hive Fleet Tiamet follows a radically different lifestyle. For some reason, these tyranids inhabit the Tiamet system and its surrounding planets, and don't fully strip them of biomass. And they guard the place very zealously, too. Every time a merchant or an exploration fleet gets close to the system, it gets inmediately swarmed by the nids. So many ships were lost that a kill team was sent to explore the area, to kno what's up with this bugs.

Ziaphoria's Tower

When the kill team arrived to the place, they discovered a massive organic towering structure (as in, the size of a continent) on the jungle forest of Ziaphoria, the largest planet in the system. What that thing does, nobody knows, but it's been speculated that is a massive psykic beacon o attract other hive fleets. The device is psykic allright, generating such a powerful Shadow in the Warp that when the first eldar appeared there, their heads almost explode from the shock of it.

Whatever this thing is, everyone in the galaxy agrees it's no good. The Ordo Xenos is extremely interested in taking this thing down, and has contacted excomunicated inquisitor Kryptman to find out what it is and how to take it down.