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"An alien threat has risen from beyond the abyss, a swarm so vast that it blots out the stars. This horror fights neither for power nor territory, but rather to feed a hunger so insatiable that it will eventually devour the entire galaxy."

Inquisitor Kryptman
Hive Tyrant - Hive Fleet Behemoth

Tyranids of Hive Fleet Behemoth attacking Imperial forces en masse

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.

The hive fleet was eventually destroyed in 745.M41 by the combined might of the Space Marines of the Ultramarines and the Imperial Navy at the Battle of Macragge.


The first documented attack of a full Tyranid hive fleet upon the Imperium was at a small Research Station on Tyran Primus. The Tyranids overran this isolated outpost of the Adeptus Mechanicus with overwhelming force, and stripped the world of all life.

By the time Inquisitor Fidus Kryptman of the Ordo Xenos arrived to investigate the strange planet-stripping phenomenon, it was already too late.

However, the adepts of the Adeptus Mechanicus who accompanied Kryptman managed to gather vital information. Before being overrun, Magos Varnak had gathered information on the alien attackers into a data codex and hid it in a bore shaft, some 3,000 metres below the planet's surface, hoping that it would be recovered later by the Imperium.

Analyzing the recovered information, Inquisitor Kryptman managed to warn the Imperium of the new xenos threat it faced. Honouring an ancient tradition of naming invading alien forces by giving them an appellation drawn from the great beasts of ancient Terran myth, this first Tyranid hive fleet was designated as "Behemoth."


The next world to fall was Occulus, a moon-sized observator station caught in Hive Fleet Behemoth's path as it pushed onwards past Tyran. The station was a bio-artefact claimed by the Imperium nine thousand standard years earlier and it was devoured, along with its Mechanicus crew.


Jagga was the homeworld of the Ork Freebooterz known as the Star Krumpas. Their considerable fleet of Kill Kroozers, once a major threat to local Imperial shipping, fought the Behemoth in a great naval engagement but was eventually destroyed.

Fate of Thandros

Behemoth and Leviathan invasion

The course of Hive Fleets Behemoth and Kraken.

Kryptman ordered his astropath to send a warning to the Imperium, but the psyker could not penetrate the Warp turmoil left by the passing of the alien fleet and its shadow in the Warp.

Even the nearby Thandros Telepathica Booster Matrix was obscured. In desperation, Kryptman set course for the Thandros System in the hopes of re-establishing communications with the Imperium there.

It was on this voyage that Kryptman realised the scale of the Tyranid threat. Following in the hive fleet's wake, Kryptman discovered a string of barren worlds that Imperial records indicated should be verdant and lush.

Reviewing a solar decade's worth of planetary survey data from that region of space, Kryptman saw a pattern emerging. He was able to plot the hive fleet's course by the trail of dead and lifeless worlds it had left behind. There was no subtlety to the hive fleet's approach, no sense of strategic genius.

It merely ploughed through the galaxy without stopping, devouring everything in its path with a rapacious hunger that would become its defining feature.

Though Kryptman's starship made good speed, the Tyranids had attacked the Thandros System and moved on long before his arrival. Thandros was not as well-protected as Tyran, and was likewise overwhelmed by the seemingly endless numbers of biohorrors that flooded its cities and fortifications.

The telepathica matrix was found to have emptied all of its turret magazines and burned out its defence laser crystal before being overrun. It was evident that Thandros had fought bravely, but its populace had nonetheless been slaughtered and consumed.


Solemnace is a Necron Tomb World ruled by the Necron Overlord Trazyn that lay in the path of two minor tendrils of Hive Fleet Behemoth.

However, the Hive Mind recognised the enormous threat presented by the Necrons, so their bio-ships made major course corrections to avoid conflict with the Necron forces on Solemnace.

Eventually, due to the inability of these tendrils to identify any biomass-rich prey worlds, these two tendrils of the Behemoth lapsed into hibernation.


It was not only the forces of the Imperium that suffered great losses due to the arrival of the Behemoth.

The world of Sybari, a Fortress World that served as the stronghold of the Death Shadows Renegade Chapter of Heretic Astartes, was also consumed by the arrival of the Great Devourer.

A Voice in the Dark

With Thandros lost, Kryptman's quest became critical. The next systems in Hive Fleet Behemoth's path belonged to the Realm of Ultramar, and unless it was forewarned, the Imperium might lose its best chance to halt the progress of the Tyranid onslaught.

With haste, Kryptman and his agents salvaged what remained of Thandros' telepathica matrix, and through a herculean effort, his astropath finally managed to pierce the shadow in the Warp to contact the unsuspecting Imperium.

The astropath, nose and ears streaming blood from the effort, broadcast Kryptman's warning. A single voice spoke back from the darkness, and it came from Macragge, the heart of Ultramar and the homeworld of the Ultramarines Chapter of Space Marines.

By the grace of the Emperor, Inquisitor Kryptman arrived at Ultramar ahead of Hive Fleet Behemoth, and met with Marneus Calgar, Chapter Master of the Ultramarines, beneath the portico of his white marble palace. Calgar stood as a giant before the Inquisitor, his stature grand even among the superhuman warriors of the Space Marines.

Calgar listened intently to the smaller man's words, but Kryptman's terrible discoveries did not disturb his noble demeanour. A true heir of the Primarch Roboute Guilliman's genius, and one of the most accomplished military leaders in the Imperium, nothing escaped Calgar's notice, not one detail about the foe that could be turned into an advantage. Hive Fleet Behemoth was fast approaching, and the Ultramarines Chapter prepared for the greatest battle in its history.

The Ultramarines were quick to react, and Marneus Calgar deployed the Ultramarine fleet to stop the Tyranid hive fleet at the garden world of Prandium -- the Jewel of Ultramar, with gardens and forests of such amazing beauty and genetic craftsmanship that it was considered one of the Wonders of the Imperium -- a world that the Ultramarines were duty-bound to protect.

Tyranids incursions

Imperial telemetry showing the paths of various Tyranid hive fleets in 998.M41.

It was a slaughter. The tactics and strategies decreed by the Codex Astartes, a tome of knowledge created by the Ultramarines' Primarch Roboute Guilliman to govern all aspects of Imperial warfare, did not succeed against the Tyranids.

The harrying strategies of the Ultramarines could not inflict enough damage against the Tyranids -- and the close-range passes of Thunderhawks and other Imperial aircraft and vehicles for optimal firepower favoured the Tyranids' mode of attack even more, since their spore cysts and clawed tentacles would burst or tear open many of the ships that went in on the attack.

The Ultramarine fleet had to sacrifice Prandium to consumption by the hive fleet. Ill-fated Calth fell next, ravaged by a smaller force of Tyranids seeded by the hive fleet's bio-ships.

For a solar week, Marneus Calgar went without food or water while meditating on the matter. When he came out of his trance-like state, he told the Ultramarines that they had been guilty of the sin of pride.

The Codex Astartes was written for the Space Marines, the Space Marines were not created for the Codex Astartes. They would have to adapt and develop new strategies and tactics, even weapons, if they were to be successful against the Tyranid menace. Hit-and-run raids were abandoned in place of concentrated defences and static firepower.

This meant that the Ultramarines had to choose a place to defend, and they chose their fortress-monastery, the Fortress of Hera, on their homeworld of Macragge, the very heart of Ultramar.

Battle of Macragge

UM 1st Co

Ultramarines' 1st Company fighting to the bitter end.

The fighting was intense, and every battle-brother of the Chapter was deployed to defend the planet. Millions of Mycetic Spores were destroyed by the planetary defences, yet millions more got through and reached the surface of the world.

Around the frozen northern laser defence batteries, Tyranid bodies stacked 10 deep. So corpse-covered was the ground, in fact, that one walked on them, and not on the frozen soil. The entire Veteran Ultramarines 1st Company was wiped out -- an enormous loss that the Chapter could ill-afford.

In space, Inquisitor Kryptman was able to discover a weakness of the Tyranid Fleet: when one of the Tyranids' major bioships was destroyed, the surrounding bioships became unable to coordinate before the arrival of a similar vessel. Striking as hard as possible, and losing many ships in the process, the Space Marines were able to destroy the Tyranid Fleet.

Unknown to the Ultramarines, Hive Fleet Behemoth was in reality separated into two forces, leapfrogging each other as they gorged on the worlds they invaded. The Ultramarines' victory at the Battle of Macragge had only destroyed half of the enemy's strength. However, the arrival of Battlefleet Tempestus, the major Imperial fleet of the entire Segmentum Tempestus, brought much-needed reinforcements.

Still, the battle was only won when Dominus Astra, the Emperor-class flagship of Battlefleet Tempestus, sacrificed itself by charging deep into the bulk of the Tyranid fleet while its Warp engines were set to overload, creating a Warp vortex that dragged it and the Tyranid fleet to oblivion. This sacrifice allowed the Imperium to finally claim victory over the Tyranid threat, at least for a short time. The Tyrannic Wars had only just begun.

It took a full Terran century for the Ultramarines to recover their full strength, and only now is the Chapter Banner of Ultramar allowed to be carried into battle forcefully once more by a full-sized Ultramarine Chapter.

Legacy of the Behemoth

Calgar Honour Guard vs

Chapter Master Marneus Calgar and his Honour Guard valiantly fight the hordes of Hive Fleet Behemoth.

The Ultramarines' Realm of Ultramar was deeply penetrated by the first Tyranid force to make contact with the Imperium, although the region lost only one of its precious worlds, Prandium.

Despite only losing one major world to the rapacious xenos, many minor worlds of the realm were consumed by Hive Fleet Behemoth, and the damage was still quite extensive.

It would take the Ultramarines nearly a standard century to recover from the loss of its entire 1st Company and much of the rest of the Chapter's forces, and the Imperial Navy also took a sizeable amount of time to recover from its losses. Also, the Tyranids left behind a deadly biological weapon in Ultramar: Old One Eye.

Though Behemoth's threat to the galaxy had ended, the Hive Mind had sampled a significant amount of new biomass during its first major incursion and gained experience in facing the strategies and operational tactics deployed by the various factions of the Milky Way. It would also be many Terran years before its creatures were scoured from Macragge and the Ultramarines replaced their losses.

After the Battle of Macragge, Hive Fleet Behemoth's survivors fractured into smaller splinter fleets that scattered in all directions. As these splinters absorbed biomass on their own, they soon grew large again, forcing the Imperium to deal with a variety of new Tyranid threats during the following solar decades.

Nevertheless, the Imperium's leaders allowed themselves to believe that the worst of the Tyranid menace was over, until it became clear during the final century of the 41st Millennium that the scattered Tyranid forces being discovered on worlds in the Eastern Fringe were the precursors of two new hive fleets, Kraken and Leviathan.

One splinter of Hive Fleet Behemoth made its way into the Adeptus Mechanicus-held world known as the Daugel Helix. Here the Mechanicus was able to use knowledge taken from the data-codex recovered from Tyran to give their cybernetic Skitarii warriors a fighting chance.

The cohort commander Alpha 9-Thyrrc turned the tide against the Great Devourer by saturating a stratum of the atmosphere with gas from the planet's promethium refineries.

After his Onager's Neutron Laser set the sky ablaze, each new wave of Tyranid spores was set aflame and incinerated the xenos already planetside instead of reinforcing them.

Though effective, this tactic was stored in another Mechanicus data-codex, brought back to the Forge World of Accatran and promptly forgotten during the battles to come.

Despite these dangers and losses, the Imperium also gained a vast amount of knowledge about the Tyranids during the First Tyrannic War. This knowledge helped the defenders of Mankind to face future hive fleets, which were soon to come, as the next threat to the Imperium was the arrival of Hive Fleet Kraken and the start of the Second Tyrannic War in 992.M41.

Notable Splinter Fleets



  • Battle Missions (5th Edition), pg. 81
  • Codex Adeptus Mechanicus - Skitarii (7th Edition) (Digital Edition), pg. 21
  • Codex: Space Marines (5th Edition), pp. 32-33
  • Codex: Tyranids (4th Edition), pp. 6, 8-9
  • Codex: Tyranids (5th Edition), pp. 8-15, 18-21, 66
  • Codex: Tyranids (8th Edition), pg. 12
  • Planetstrike (5th Edition), pg. 54
  • Warhammer 40,000 Chapter Approved - The Book of the Astronomican
  • Warriors of Ultramar (Novel) by Graham McNeill
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