Hive Fleet - Primary Hive Fleets: Hive Fleet Behemoth  - Hive Fleet Behemoth was the first major Tyranid hive fleet encountered and defeated by the Imperium of Man. The ensuing conflict became known as the First Tyrannic War. This hive fleet was eventually destroyed in 745.M41 by the combined might of the Ultramarines, the White Scars, and the battlefleets of the Navis Imperialis.Hive Fleet Kraken - Hive Fleet Kraken was the second major Tyranid hive fleet to invade the galaxy. It was responsible for the outbreak of the Second Tyrannic War, which began officially in 992.M41 and ended only after the Ultramarines Chapter of Space Marines successfully broke the back of the Tyranid invasion in Imperial space at the Battle of Ichar IV and the Asuryani of Craftworld Iyanden successfully defended their home, at great cost, against the Tyranid horde.Hive Fleet Leviathan - Hive Fleet Leviathan was the third and largest Tyranid incursion into the Milky Way Galaxy in 997.M41 and marked the start of the Third Tyrannic War for the survival of the Imperium. Less than five standard years after the defeat of Hive Fleet Kraken in the Second Tyrannic War, 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 galaxy. Codenamed "Leviathan", this time the Tyranids approached 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 the Adeptus 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 Imperial worlds between Leviathan's jaws. The Imperium had won its first victory in a war that had only begun. Later, during the Era Indomitus, the Blood Angels and their successors among the Sanguinary Brotherhood defeated a massive tendril of the Leviathan with the aid of the Daemons of Khorne's Blood Legions commanded by the Bloodthirster Ka'Bandha and the Indomitus Crusade of Roboute Guilliman at the Battle of Baal. Unfortunately, the Hive Mind had only begun to intensify its final push against the Imperium. It was not long after the fighting on Baal that 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, the start of the Fourth Tyrannic War, 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.