Event · M41
Behemoth Invasion
The Behemoth Invasion was the assault of Tyranid Hive Fleet Behemoth on the Ultramarines’ realm of Ultramar, centred on Macragge, in 745.M41. It is the opening episode of the First Tyrannic War and is recorded as the first large-scale Imperial encounter with the Tyranids, an extragalactic swarm that consumes the biomass of the worlds it reaches. The fleet is held to have entered the galaxy from beyond its eastern fringe and to have advanced towards the Imperium’s heartlands, and Ultramar lay directly in its path. The Ultramarines, led by Chapter Master Marneus Calgar, made the defence of Ultramar their Chapter’s principal effort, drawing on the Imperial Navy and the planetary forces of the Ultramar worlds. Accounts identify Chief Librarian Varro Tigurius and Captain Cato Sicarius among the Chapter’s notable participants, and place the decisive fighting on and around Macragge. The Tyranids were opposed by fortified positions, void engagements and a sustained ground campaign, and the disruption of the fleet’s synaptic control is recorded as central to the defenders’ success. Exact tallies of forces and of individual engagements vary between accounts and are not treated here as fixed. Behemoth is recorded as broken at Macragge, though fragments of the fleet are said to have persisted for a time afterwards. The Ultramarines are held to have paid a heavy price in battle-brothers and war material, and the campaign strengthened the Chapter’s standing as the Imperium’s foremost authority on the Tyranid threat. Later swarms, among them Hive Fleets Kraken and Leviathan, are regarded as separate incursions from the same extragalactic source, and the events of 745.M41 remain the reference point against which subsequent Tyrannic Wars are measured. On the Orrery map the invasion is anchored to Macragge in Ultramar, and on the timeline to the First Tyrannic War in the forty-first millennium.
See where Behemoth Invasion occurred on the galactic map in the 41st Millennium.