Either that, or they realised that to use such weapons would probably destroy the bridge.

Most of the Space Marines who had been caught in the open were in cover now and Uriel knew they were lucky not to have lost more men. He cursed as he saw the lumbering shape of Sevano Tomasin still fixing explosive charges and unwinding lengths of cable back towards the last bunker. The Techmarine's movements were painfully slow, but he was undaunted by the shelling. Uriel willed him to work faster.

'One and a half kilometres and closing. Closing rapidly! Dismounted enemy infantry visible!' shouted the scout sergeant in Uriel's comm-bead.

'Acknowledged,' shouted Uriel over the crash of falling mortar shells and explosions. 'Get back here now: there's nothing more you can do from there. Sword squad is waiting at the first bunker to give you covering fire. Ventris out.'

Uriel and Idaeus reached the bunker and splashed to a halt behind its reassuringly thick walls. Idaeus snatched up his vox-com and shouted, 'Guard command net, this is Captain Idaeus, Ultramarines Fourth Company. Be advised that hostiles are attacking across Bridge Two-Four in division strength, possibly stronger. We are falling back and preparing to destroy the bridge. I say again, hostiles are attacking across Bridge Two-Four!'

As Idaeus voxed the warning to the Imperial Guard commanders, Uriel patched into the frequency of the Thunderhawk that had dropped them in position.

'Thunderhawk Six, this is Uriel Ventris. We are under attack and request immediate extraction. Mission order Omega-Seven-Four. Acknowledge please.'

For long seconds, all Uriel could hear was the hiss of static and he feared something terrible had happened to the gunship. Then a voice, heavily distorted said, 'Acknowledged, Sergeant Ventris. Mission order Omega-Seven-Four received. We'll be overhead in ten minutes. Signal your position with green smoke.'

'Affirmative,' replied Uriel. 'Be advised the landing zone will in all likelihood be extremely hot when you arrive.'

'Don't worry,' chuckled the pilot of the gunship. 'We're fully loaded. We'll keep their heads down while we extract you. Thunderhawk Six out.'

Uriel snapped the vox-unit to his belt and hammered on the bunker's door. He and Idaeus ducked inside as it slid open. The five Space Marines within were positioned at the bunker's firing step, bolters and a lascannon pointed at the hills above, ready to cover their brothers' retreat. Uriel stared through the anti-grenade netting, watching the scouts falling back in good order towards the bridge.

'As soon as the scouts are past you, fall back to the first gun nest and take up firing positions,' ordered Idaeus. 'The other squads are already in position and they'll cover you. Understood?'

The Space Marines nodded, but did not take their eyes from the ridge above the approaching scouts. Idaeus turned to Uriel and said, 'Get across and see how close Tomasin is to blowing this damned bridge. We'll join you as soon as we can.'

Uriel opened his mouth to protest, but Idaeus cut him off, 'Stow it, sergeant. Go! I'll join you as soon as Alpha Team are safe.'

Without another word, Uriel slipped from the bunker. Another series of thunderous detonations cascaded across the bridge and impacted on the sides of the gorge. Uriel waited until he detected a lull in the firing then began sprinting across the bridge, weaving around piles of rubble, debris and water filled craters left by the explosions. He could still see Sevano Tomasin behind the sandbagged gun nests, working on the detonators.

He heard gunfire behind him, the distinctive, dull crack of bolter fire and the snapping hiss of lasguns. He glanced over his shoulder as a terrible sense of premonition struck him.

Twin streaks of shrieking projectiles flashed overhead, one landing behind him and another before him with earth shaking detonations. The first shell exploded less than four metres above the men of Alpha team, shredding their bodies through the lighter scout armour leaving only a bloody mist and scraps of ripped flesh. The shockwave of the blast threw Uriel to the ground. He coughed mud and spat rainwater, rising in time to see Sevano Tomasin engulfed in blinding white phosphorescent fire.

The Techmarine collapsed, his metal limbs liquefying and the flesh searing from his bones. A second melta charge ignited in his equipment pack, also cooked off by the mortar shell's detonation. Tomasin vanished in a white-hot explosion, the rain forming a steam cloud around his molten remains.

Uriel pushed himself upright and charged towards the fallen Space Marine. Tomasin was dead, there could be no doubt about that. But Uriel needed to see if the detonator mechanism had gone up with him. If it had, they were in deep, deep trouble.

Idaeus watched the first squadron of enemy vehicles crest the ridge above, hatred burning in his heart. Even in the fading light, he could clearly make out the silhouette of three Salamander scout vehicles and Idaeus vowed he would see them dead.

He could smell the acrid stench of scorched human flesh from the blasted remains of the scouts. They had died only ten metres from the safety of the bunker. Idaeus knew he should fall back to the prepared gun positions further along the bridge: if they stayed here much longer, they'd be trapped. But his thirst for retribution was a fire in his heart, and he was damned if he would yield a millimetre to these bastards without exacting some measure of vengeance for his fallen warriors.

'Nivaneus,' hissed Idaeus to the Space Marine carrying the lascannon. 'Do you have a target?'

'Aye, sir,' confirmed Nivaneus.

'Then fire at will. Take down those traitorous dogs!'

A blinding streak of las-fire punched from the massive weapon. A Salamander slewed from the road, its hull blazing and smoke boiling from its interior. The vehicles' supporting infantry squads fired their lasguns before the Space Marines' bolter fire blasted them apart with uncompromising accuracy. But Idaeus knew they were inconsequential. Killing the tanks was all that mattered.

Nivaneus calmly switched targets and another Salamander died, its crew tumbling from the burning escape hatches. The last tank ground to a halt, stuttering blasts from its auto-cannon stitching across the bunker's face. Idaeus felt the vibrations of shell impacts. He smiled grimly as the Salamander's driver desperately attempted to reverse back uphill. Its tracks spun ineffectually, throwing up huge sprays of mud, unable to find purchase. Dust and an acrid, electric stench filled the air as Nivaneus lined up a shot on the struggling tank.

Before he could fire, a missile speared through the rain and smashed into the immobilised tank's turret. It exploded from within, wracked by secondary detonations as its ammo cooked off.

'Captain Idaeus!' shouted Uriel over the vox-net. 'Get out of there! There will be more tanks coming over that ridge any moment and you will be cut off if you do not leave now! We have you covered, now get back here!'

'I think he's got a point, men,' said Idaeus calmly. 'We've given them a bloody nose, but it's time we were going.'

The Ultramarines fired a last volley of shots before hefting their weapons and making for the door.

'Uriel!' called Idaeus. 'We are ready to go, now give me some fire.'

Seconds later a withering salvo of bolter fire and missiles swept the ridge top, wreathing it in smoke and flames. Idaeus shouted, 'Go, go, go!' to the Space Marines and followed as they sprinted through the rain. The mortar fire had ceased: probably due to the Griffon tanks being moved up into a direct firing position, thought Idaeus. Whatever the reason, he was grateful for it.

He heard a teeth-loosening rumble and a squeal of tracks, knowing without looking that heavy tanks had spread out across the ridge, moving into a firing position behind them. He saw two missile contrails flashing overhead and heard the ringing clang of their impact. A crashing detonation told him that at least one enemy tank was out of action, but only one.