Hive Fleet Leviathan is the largest and greatest Tyranid Hive Fleet to invade the Galaxy. It attacked in 997.M41 from the galactic south.
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Hive Fleet Leviathan is the largest and greatest Tyranid Hive Fleet to invade the Galaxy. It attacked in 997.M41 from the galactic south. Unlike the majority of previous Hive Fleets that attacked from the Eastern Fringe, Leviathan instead skirted under the galactic rim of the galaxy and then pushed upwards through the galactic plane, spreading its forces across a broad front that covered the Ultima Segmentum, Segmentum Tempestus and even into the Segmentum Solar. Leviathan’s strategy was to form its forces into two giant tendrils hundreds of light years apart in such a way that it stretched the Shadow in the Warp over the vast distance between the two tendrils, stopping all psychic contact between the trapped worlds and the Imperium and also blocking Imperial reinforcements from navigating the Warp towards the beleaguered worlds.
One of Leviathan’s main tendrils, which was on a projected course directly to Terra, was eventually stopped at Tarsis Ultra. However, Leviathan as a whole remained undefeated and continued to assault the galaxy. Leviathan consumed countless worlds. In response, the Imperium is reinforcing entire Systems, raising thousands of armies and dispatching dozens of Space Marine Chapters to troubled areas; meanwhile, several Craftworlds of Eldar used ancient destructive weaponry to reduce planets to Dead Worlds, and the Tau developed new technologies and weaponry to combat the Tyranids. Thanks to the formation of the Great Rift, much of Leviathan was cutoff as it made its main assault on Baal, homeworld of the Blood Angels. Most of Leviathan was destroyed during the period known as the Blackness against the defenders of Baal, the Indomitus Crusade, and newly materialized Daemonic armies.
In late 997.M41 the Imperium first lost contact with several systems in the Segmentum Tempestus. Inquisitor Kryptman implemented a great astrotelepathic augury, which became known as the Kryptman Census, and eventually made contact with every documented planet on the southern fringe of the Imperium. The worlds that ceased to respond began to form a pattern, and Kryptman identified it as the approach of a hive fleet of terrifying size. Leviathan’s principle attack formed two tendrils hundreds of light years apart. The Imperium lost contact with the worlds trapped between these two “jaws”, and if these jaws closed they would devour all trapped inside.
The planet of Tarsis Ultra stood directly in the path of one of Leviathan’s main tendrils, the tendril on a course towards Terra. Tarsis Ultra was defended by the Ultramarines led by Captain Uriel Ventris, along with the aid the Mortifactors led by Chaplain Astador, and supported by the 10th Logres led by Colonel Octavius Rebalaq, the 933rd Death Korps of Krieg led by Colonel Trymon Stagler, and PDF Regiments headed by Major Satria. Inquisitor Kryptman was also present to impart his extensive knowledge of the Tyranid threat. Tarsis Ultra was besieged for several weeks, only just managing to hold out under the command of Uriel Ventris and later Kryptman. The tides eventually turned in Imperial favour when Ventris and a Deathwatch Kill-team captured a Lictor from the original wave of the invasion. Magos Biologis Vianco Locard reverse engineered the Lictor’s genetic code to design a biological plague that would send an early generation Tyranid into hyper-evolution and thus kill the creature. If delivered to the heart of the swarm it could destroy the entire tendril. Ventris then joined the Deathwatch team in infiltrating the final remaining Hiveship and delivered the plague to the Norn-Queen. Slowly at first, but with gathering speed, the Tyranids turned upon and attacked each other. Their synaptic control had been lost. At this point, the remaining Space Marine contingent of both the Ultramarines and Mortifactors were down to sixteen men. The majority of the remaining Tyranids froze to death under the harsh conditions of Tarsis Ultra with a minority surviving and taking refuge in warmer surroundings. The Imperial forces launched a counter-offensive which destroyed the swarm and stopped the invasion. Leviathan’s tendril, on a course to Terra, was dissipated and the once-doomed worlds caught in between Leviathan’s two main tendrils began to register on Imperial augurs again.
Leviathan continued its assault on the galaxy. Two dozen Space Marine Chapters were known to be involved in containment operations, with Captain Aajz Solari of the Raven Guard in overall command. As of 997.M41 Imperial Guard Army Group Twelve, comprised mainly of Catachan and Jornian forces, continued to hold out against a tendril as reinforcements were being raised. In 999.M41 a tendril of Leviathan was identified to be on a direct course to the Blood Angels’ Homeworld of Baal. Despite a delaying action in the Cryptus Campaign, Baal eventually came under Tyranid invasion. The Tyranids were on the verge of victory until the Great Rift formed as a result of the Thirteenth Black Crusade and its aftermath. The sudden Warp Storms cutoff most of Leviathan inside the Baal System, while great Daemonic hosts surged into the Materium. Nonetheless, the Tyranids were on the verge of victory on Baal until the arrival of the Indomitus Crusade led by Roboute Guilliman itself. After many battles, the devastated world of Baal and its two moons were won. What became of much of Leviathan remains mostly a mystery, swept up in the period of chaos known as The Blackness. What is gathered however is that newly formed Daemonic forces moved against the xenos. On Baal’s moon of Baal Prime the symbol of the Bloodthirster Ka’Bandha was formed from the skulls of many fallen Tyranids.