Inquisitor Kryptman received word of the last message from Tyran months after the attack. By the time his ship reached the Tyran system almost a year had passed and at first he could not equate the dead, dry planet he found to ocean-bound Tyran at all. After a long search Inquisitor Kryptman unearthed Varnak's data codex and learned the full horror of the alien threat menacing the Imperium.

As the Inquisitor's ship left the Tyran system it encountered the acid-eaten hulk of the investigation, declared missing months before. The vessel appeared to have been crippled and then boarded: all of the crew were missing and the ship was little more than an icy shell. Clearly the same foe that attacked Tyran had destroyed the Investigation and perhaps even followed its trail through the warp back to the Tyran Primus base.

Kryptman ordered his Astropath to send a priority warning to the Imperium but the Astropath could not penetrate the warp turmoil left by the passing of the alien fleet. Even the nearby Thandros telepathica booster matrix was obscured. In desperation Kryptman set course for Thandros in the hopes of re-establishing communications there.

But the Tyranids had attacked Thandros and moved on long before the arrival of Inquisitor Kryptman. Thandros was not as well protected as Tyran. The miners living in tunnels on Thandros II and III could not hide from the Tyranids or escape into space. The telepathica matrix orbiting Thandros I was later found to have emptied all of its turret magazines and burned out its defense laser crystal before it was overrun. Nonetheless the Telepathica adepts manning the base were unable to send word of their plight to the Imperium because of the Tyranids' psychic blockade. The Thandros system fought and died alone.

Kryptman salvaged the telepathica matrix and sent his message to warn the unsuspecting Imperium of the magnitude of the Tyranid threat. The Astropath, red-eyed with weariness after days of concentration broadcasting Varnak' s codex and Kryptman's report, gave the Inquisitor instructions to travel to the planet Macragge in Ultramar, the empire of the Ultramarines Chapter of the Adeptus Astartes. There he would assist the Master of the Chapter in locating and eliminating the Tyranid fleet. As dictated by Imperial tradition the alien hive fleet of the Tyranids had been codified with an ancient and forbidding name from legend: Behemoth.

The Navigator of Kryptman's ship strained to follow the guiding light of the Astronomican through the swirling energies of warp space as the ship pushed through the shoals and reefs of that most capricious medium. At times the undertow left by Hive Fleet Behemoth threatened to lose the ship in the warp forever but the Navigator avoided every whirlpool and riptide with consummate skill, the elongated teardrop formed by the warp drives of the Inquisition ship slipping through the Immaterium like oil through water.

In the Macragge system a dozen other ships already hung in orbit and each day more arrived from the warp. Lumbering Space Marine battle barges hung over Macragge like gigantic azure monoliths etched with the gaping maws of weapon bays, launch tubes and heavy bombardment turrets. These leviathans dwarfed even the sleek strike cruisers arriving from the Ultramarines' furthest outposts. Orbital fortresses and ponderous systems defense monitors surrounded Macragge with a ring of firepower.

Inquisitor Kryptman met with Marneus Calgar, Master of the Ultramarines, beneath the portico of his palace of brilliant white marble perched high in rugged mountains above the glittering seas of Hera. Calgar stood as a giant even among the genetically altered Space Marines. Nothing escaped his piercing blue eyes and even Kryptman' s terrible discoveries did not disturb his noble demeanor.

The Ultramarines were readying themselves for all-out war with the Tyranids. The Emperor had dispatched a Segmentum Tempestus battlefleet from the orbital docks at Bakka. Calgar felt that Macragge was the system most immediately threatened by hive fleet Behemoth. Macragge itself, already well-protected, was being even more heavily fortified and would be held tenaciously by Ultramarines and planetary defense auxilia until the combined Ultramar and Imperial fleet arrived to take on the hive fleet.

A month later the Tyranids attacked Macragge, their fleet of over a thousand vessels sweeping aside attacks by Ultramarines strike cruisers as they pushed in system. With no sign of the Imperial fleet from Bakka, Calgar was forced to use the Ultramar fleet in a risky ploy. By leaving Macragge and retreating out system Calgar drew the Tyranids onto the defences of Macragge as they sought to encircle it and invade. The Ultramar fleet struck the aliens while they were spread out and vulnerable, successfully carving a bloody swathe through their fleet as Calgar tried to fight his way back through to the protection of the big guns of Macragge.

At the height of the battle Ultramar fighters from Macragge crippled one of the largest Tyranid hive ships and this seemed to fatally disrupt the cohesion of the hive fleet. The Tyranids' attacks became increasingly uncoordinated and Calgar's fleet reaped a great tally of fallen bio-ships. As the battle raged the Tyranids unleashed thousands of spores above the vital northern and southern polar fortresses which were the keystones of Macragge's defences. Each spore that fell to earth cracked open to reveal a Tyranid creature and soon thousands of Tyranids were marching across the ice fields towards the fortresses.

In space the battered hive ships retreated and, desperate to prevent their escape, Calgar' s tiny fleet gave chase. Though Calgar feared for the polar fortresses he knew they were well guarded by Ultramarines of the 1st Company supported by defense auxilia and Titans of the Legio Praetor. Most of the 1st Company were formed into Terminator squads equipped with tactical dreadnought armour and the best personal weaponry in the Imperium. Entrusting the fate of Macragge to these veteran warriors, Calgar chose to pursue the Tyranid hive fleet.

The Tyranid swarms on Macragge surged on towards the polar fortresses. Sickle-clawed beasts bounded forward across snowy plains scored by lasers, their numbers blurring individuals into a shifting mass of slicing hooks and piercing talons, others wheeled through the bleak, grey skies on leathery wings and drooled their liquid fire on the defenders below. The ear splitting rattle of bolters and the thump of artillery drowned out the bestial, hate-filled screams of the swarming Tyranids but they swept on with implacable ferocity.

The veteran Space Marines of the 1st Company led the lightly armed defense auxilia in a tenacious defense of the fortresses, holding every wall and trench until the last possible moment before it was overrun by the swarm. Slowly the troops withdrew ever deeper into the fortress while making the Tyranids pay in blood for every yard of ground. The Titans of Legio Praetor stalked the ice fields and drove smoking furrows through the onrushing Tyranid hordes with shells and plasma. Crippled Ultramarine ships which Calgar had left in orbit above hurled down bolts of ruby flame and megatons of explosive death at the Tyranids, but still they came on.

The ferocity of the swarms was unbelievable. At the northern fortress they overran the walls by using the steaming piles of their own dead for cover. Titans were dragged down and ripped apart by sheer weight of numbers, like lions being swarmed over by soldier ants. Weapon barrels glowed red hot and jammed in spite of the arctic cold, ammunition began to run low though the fortress contained stockpiles for months of siege. The snows around the fortresses were stained arterial purple with Tyranid ichor.

As the fighting became close and deadly lumbering scythe-armed giants tore into the defenders' ranks like living battering rams, smashing their way through metal and rockcrete walls with equal fury. Even the Terminators could not stand against Tyranids in hand-to-hand fighting. Six-limbed, armed and armoured in shining chitin, the creatures sprang forward with blinding swiftness, their claws lashing out to rip through ceramite and adamantium with impossible ease. The Ultramarines had to rely on the heavy short-range firepower of their storm bolters, heavy flamers and Assault cannon to bring down the foe.

At the southern fortress stalking creatures penetrated deep into the labyrinthine corridors beneath the citadel through a supposedly inaccessible disposal culvert. The mantis-clawed horrors slew dozens of auxilia troopers from ambush in the maze of dark corridors and rooms before they were finally hunted down and eliminated by Terminator squads. Some men were driven mad with fear or paralysed with terror as the Tyranids broke through the perimeter again and again. With each perimeter breach the Ultramar garrisons had to withdraw to a new defense line. The Ultramarines were forced back, step by step, by the alien tide of organic killing machines.

In space Calgar pursued the Tyranid fleet toward the ringed world of Circe at the edge of the Macragge system. The timely arrival of the Tempestus fleet from Bakka finally sealed the Tyranids' fate by catching them in a vice between the two fleets. In a desperate fight the combined human fleet destroyed the remaining hive ships at a great cost in men and ships.

The Tempestus fleet of over two hundred warships including the huge Emperor class battleship Dominus Astra was almost completely wiped out in a titanic battle around Circe. The battle was only won by the heroic sacrifice of the Dominus Astra charging into the heart of the hive fleet and triggering it's warp drives. The Tyranids were destroyed in an uncontrolled warp vortex which also dragged the Dominus Astra into oblivion. Calgar's surviving ships came about and roared back to Macragge to try and save the beleaguered polar garrisons.

The remnants of the Ultramar garrisons had been forced deep underground by wave after wave of Tyranids. The survivors of the Ultramarines 1st Company were still fighting amongst the coolant stores and capacitors of the giant defense laser silos of the northern citadel but all contact with them was lost after the Tyranids completely overran the surface outposts. At the southern fortress the remaining 1st Company detachments had been destroyed when they attempted a counter-attack against a vital bastion captured by the Tyranids. Small pockets of Ultramar resistance still held out in bunkers above ground. Calgar, feeling that the situation was becoming critical, sent the 3rd and 7th Ultramarines Companies ahead in their fast strike cruisers while his remaining damaged ships limped back to Macragge.

As the sleek strike cruisers swooped over Macragge the Space Marines of the 3rd and 7th Companies were deployed by drop pod onto the poles with their supporting units following up in gunships. Scenes of unbelievable carnage awaited them below. Piles of mangled Tyranid corpses and shattered wargear lay strewn across the ice. Vast steaming craters pocked the snows where Titan plasma reactors had melted down and the stench of death lay everywhere.

The 7th Company, dropping on the southern fortress, landed unopposed and quickly linked up with the survivors of the garrison above ground. Together they pushed on to clear the subterranean passages which had been overrun. Only a handful of Tyranids remained to oppose them but they fought back with maniacal ferocity. Initial progress was bloody, with several advance squads being attacked by lone Tyranids or small groups which took their toll. But the Tyranids' attacks lacked strategy or coordination and most of the creatures were riddled with bolter fire as they emerged from cover.

In the north the 3rd Company came under attack as soon as it landed. Hundreds of creatures emerged from dark tunnel mouths and shattered bunkers to assail the Space Marines, threatening to overrun their dropzone by sheer force of numbers. Only staunch defensive fire laid down by the company s Devastator squads kept the alien swarm at bay until Thunderhawk gunships arrived to blast the Tyranids back below ground. Captain Fabian of the 3rd Company prudently awaited the arrival of the company's three Dreadnoughts before proceeding into the fortress itself to search for survivors.

The dark, dank corridors beneath the northern fortress were already subtly altered by the aliens' presence. Mucous dripped from the walls and ceilings and a pervasive musky stench filled the air. Alien screams and roars echoed and re-echoed weirdly along the tunnels. Warily, the Space Marines pushed forward, the darkness moving back reluctantly before their suit lights. The corridors were littered with Tyranid and Ultramar dead and even bio-scanners failed to identify the creatures that lay in ambush amongst the corpses. Such lone attackers wreaked havoc at close quarters, slashing into the advance squads in an orgy of destruction before they were killed.

Eventually the forward squads started to use flamers to burn their way along the passages and flush out their enemy. Even as the creatures burned they still leapt forward with claws outstretched to rip and slay.

Two full squads of Space Marines were killed in a lightning fast flank attack by a dozen Tyranids at an intersection. Only the presence of a Dreadnought blocked their rampage through the company's perimeter, and the Dreadnought itself had one arm ripped off by the creatures before it cut through them with its assault cannon. As the company entered a great chamber below Silo 8 they were assailed from all sides as a nightmarish horde of creatures sprang from the shadows.

A hail of obscene projectiles struck at the Space Marines, burning through their armour and spraying them with vile corrosive mucous. Chain swords clashed against curving blades of bone and bolters chanted their catechism of death as the Ultramarines desperately fought back. A mighty Tyranid lord, huge as a Dreadnought, thundered into the Space Marines' line. Three Space Marines fell to a single sweep of its curving blade before a Dreadnought charged into the monster.

A titanic struggle ensued as monster and machine battled to the death. The Dreadnought reeled back as the Tyranid struck it a mighty blow, sparks flew as the Dreadnought's power fist crashed into beast's carapace. Pouring ichor from its wounds the creature raised its blade and chopped through the machine's leg to send it crashing to the ground.

The beast howled in triumph and raised its blade to deliver the killing blow as Captain Fabian leapt forward into the fray. Power sword and alien blade clashed together with a cracking energy discharge. The beast swung a mighty overhead blow at Fabian as he staggered back from the discharge but the captain leaped aside and the blade buried itself in the rockcrete floor with a flash of power. In the fraction of a second before the creature freed its blade Fabian leveled his plasma pistol at the creature and fired, the incandescent blast catching it full in the head as Fabian pumped shot after shot into the creature. The beast reared up with a final ululating howl of agony and fell back dead.
All around, the Ultramarines were on the verge of being overwhelmed, only the psychic blasts of the Librarian were stopping the Tyranids completing the slaughter. But as the Tyranid lord fell many of its minions turned tail and were cut down by bolters as they fled. Those that fought on were blasted apart as the Ultramarines resorted to firing amongst their own troops to finally prevail. At the end of the fight barely a quarter of the company had survived and all three Dreadnoughts were damaged. Captain Fabian grimly ordered his remaining men to continue the hunt for survivors.

Once more the greatly reduced company cleared its way forward with flamers and finally reached the lower penitorium where the 1st Company had made their last stand. Tyranid bodies were piled six deep around the doors and within the room a circle of Terminators lay where they had fought hack to back. They were still and lifeless, every one having given his life against the Tyranid hordes. The Ultramarines' 1st Company had been wiped out to the last man, a grievous blow from which the Chapter has still to fully recover.
Hive Fleet Behemoth had been stopped, but only at a grievous cost to the Imperium of Mankind. In the aftermath of the first Tyrannic war there was little the Imperium could do to strike back at its foe. Behemoth had arrived from a virtually unexplored quarter and had disappeared completely after the Battle of Macragge. The trail of the hive fleet led back to the empty void of intergalactic space.

The Techno Magi of Mars spent many years classifying the Tyranid artifacts and bodies left on Macragge but could divine little from the evidence. The obvious facts were that, like the Eldar, the Tyranids used a form of bio-technology to organically form weaponry (though Tyranid weapons were limited to short-ranged projectiles and close combat weaponry) and that the Tyranids themselves formed an incredibly diverse race, more so than even the Orks. Gretchin and Snotlings which infest the galaxy.

The only discovery of great note was that the Tyranids had employed Genestealers as shock troops. These creatures had previously been thought to be autochthonous denizens of the moons of Ymgarl that had spread through space onboard cargo barges. Their presence amongst the Tyranid hordes was testament that this theory was in error. Genetic samples indicated they were Tyranid creatures, so why were they already established far to the galactic north-west? The Salamanders Chapter of Space Marines conducted a genocide campaign to purge the moons of Ymgarl and Inquisitors intensified their scrutiny for Genestealer infestations but nothing more could be done.