'I'm too close for a missile shot!' he yelled, switching to guns as the creature tried to shake him.

Every move the creature made, the Fury was with it, spinning around like insects in a bizarre mating ritual. The beast flashed across his gunsight and he pulled the trigger.

'Got you, you bastard!' he roared as bright lasbolts ripped the tyranid beast in two.

'Captain! Break right!' screamed Pelaur as a spuming bolt of light speared past the Fury's canopy.

He pulled around and breathed deeply, amazed at how close their near miss had been. He eased back on the throttle and switched back to missiles.

A warbling tone in his ear told him the missile's war-spirit had found a target and he pulled the trigger again.

'Captain!' called Erin Harlen. 'You've got one right behind you!'

Morten hauled right and checked his rear, twisting his Fury in an attempt to shake the pursuing organism.

'I can't get rid of it!' swore Morten as the beast matched his wild manoeuvrings.

'It's firing!' shouted Pelaur.

'Breaking left!' answered Morten, rolling hard and kicking in the afterburner. He felt his flight suit expand and his heartbeat race.

A bolt of crackling energy spat below him and he spun the plane round in a screaming, tight turn, chopping the throttle and almost stalling the engine.

The creature tried to match his turn, but was too slow.

Morten rolled inverted and pulled in behind the pulsing organism, lining it up in his sights and firing.

Bolts from the lascannon shredded the creature and it exploded in a bloody spray.

Listening to the vox-chatter, he heard screams and imprecations from the rest of the aircraft. The tyranids were slaughtering them, but he couldn't think about that just now. Not while there was a battle still to be fought. But as he scanned the space before him, he could see they'd blown a gap. The Thunderhawk was streaking through it, the blue glare of its plasma engines bright against the darkness of the massive hive ship's stony carapace.

Then he saw a giant, winged creature with spitting, electrical mandibles powering after the Space Marine gunship. Arcs of crackling energies lashed the Thunderhawk again and again, and Morten could see it wouldn't survive much longer.

His flight suit was soaked with perspiration and he knew he was at the edge of exhaustion, but he pushed out the engines to follow the Thunderhawk.

Uriel felt the gunship lurch, and leaping streaks of blue energy sparked from the fuselage. The pilot threw them in a series of wild turns, but Thunderhawks had never been designed for dogfights and Uriel knew it was only a matter of time before whatever was pursuing them was able to destroy them. Weapons and ammo packs tumbled from the lockers above him.

He pushed clear of the restraint harness and rose to his feet, turning to retrieve the weapon Inquisitor Kryptman had given him. To lose it now would end their mission before it had begun. He staggered as another impact smashed into the gunship. Flames erupted from a shattered fuel line and warning klaxons screamed.

Yet another hammer-blow struck the rear quarter of the Thunderhawk and one of the vision ports blew out with a decompressive boom.

Rushing air howled from the gunship, and Uriel felt his rage growing. They could not fail. Not after coming so close.

But as further impacts rocked the Thunderhawk, he knew they could not survive another.

Captain Owen Morten pushed the Fury as fast as it could go. His fighter streaked past the tyranid organism pummelling the Thunderhawk as he armed the last of his missiles.

A flickering blue glow illuminated the interior of the Fury as bolts of lightning lashed from the mandibles of the creature. Fully six times the size of the Fury, Morten knew that only a direct hit on its most vulnerable location would destroy it.

'Captain!' shouted Pelaur, 'ease back on the throttle or we won't have enough fuel to get back to the planet.'

'We're not going back,' said Morten calmly as he neatly slotted the Fury between the giant tyranid beast and the Thunderhawk.

'What the hell are you doing?' screamed Pelaur.

'What needs to be done,' answered Morten, cutting the engines and spinning the Fury on its axis until it had turned a full one hundred and eighty degrees.

The crackling maw of the tyranid beast filled his canopy. Giant arcs of lighting enveloped the Fury. Sparks and flames filled the cockpit.

Captain Morten pulled the trigger, sending his last missile straight down the monster's throat.

Uriel felt a huge detonation behind the gunship, and awaited the inevitable destruction of the Thunderhawk. But the fatal blow never landed and the Thunderhawk levelled out, weaving through the hail of spores that gathered around the monstrous hive ship.

He made his way up the central aisle of the gunship towards the cockpit. All he could see ahead was the craggy cliff of the hive ship's hide. Inquisitor Kryptman had shown them the most likely locations of possible entry points, and he scanned the grey moonscape before him for one.

The aerial armada had got them through and now it was time to make good on that sacrifice.

'There!' he said, pointing to a rippling, fleshy orifice on the side of the gargantuan creature, organic waste venting through it into space by peristaltic motion of flesh. A ribbed sphincter muscle expanded as more waste was expelled and Uriel knew they had found what they had come for.

'Hurry! If what Inquisitor Kryptman says is true, it will close in seconds!'

The pilot deftly guided the gunship forward, increasing power to the engines as the fleshy orifice began to contract.

Only as they approached did Uriel realise how vast it was, fully sixty metres in diameter.

Before it could close completely, the Thunderhawk sped into the ribbed, fleshy tunnel beyond.

Truly they were in the belly of the beast, thought Uriel as the sphincter vent closed and the faint light of the stars was snuffed out.

Learchus swept his chainsword through the neck of yet another tyranid creature, his blade clogged with alien meat and gristle. His bolter had long since run out of shells and he fought two-handed with his blade.

Clotted blood caked his shoulder where a screeching monster twice the height of a man had gained the walls and torn through his armour. The wall was a charnel house of alien and human dead. Cracked pillars and columns clustered at the wall's edge were hung with gory spatters of blood and entrails that spilled over the icy ground, making it treacherous underfoot. Learchus fought for balance with every step he took.

Major Satria fought alongside him, stabbing with his bayonet and firing with his lasgun whenever he had the chance to reload. Beside him, Fabricator Montante fought with desperation and courage, if not skill. Learchus had already saved his life on numerous occasions and though it was foolish of Montante to be here, he was forced to admire his bravery.

'Warriors of Ultramar hold fast!' bellowed Learchus.

Drifting spores exploded amongst the battling warriors, but they refused to give way. He kicked out at a screeching hormagaunt as it scrabbled over the lip of the wall, sending its shattered skull spinning to the heaving mass of aliens below.

Over the deafening clash of battle at the wall, Learchus heard the roar of guns behind him and risked a glance over his shoulder to see who was shooting. The few remaining Hydra flak tanks were firing eastwards and his hearts skipped a beat as he saw the impenetrable black cloud of gargoyles sweeping down the length of the valley.

'Guilliman save us…' whispered Learchus as he took in the numbers of enemy now closing on their rear.