Siege of Vraks - Into the Undercroft: Whilst the assault raged across the ruins of the Citadel, deep below the engineers of the Krieg regiments began their own battle. They had undermined the Citadel rock; it had taken them over six years of work, digging, digging, always digging, until they had cut their way through forty kilometres from the inner defense line all the way to the Citadel. Their Hades drills and breaching charges smashed through the last few metres of rock and into the depths of the Citadel and its armoury.Much like an iceberg, what was visible of Vraks’ Citadel was only a small part of the whole. The Basilica and other surface buildings were all impressive architecture in the grand style of the Imperium; a physical statement of great power, but the workings of the Citadel were below ground. Kilometres of dim, dark corridors and galleries, storerooms and archives, the great geo-thermal heat wells that drew energy from the planets massive transformer chambers thrummed with energy as they harnessed the power and then distributed it via underground cables to the rest of the planet At the base of the rock, the Citadel was actually a power station, next to which were the banks of void shield generators that sucked up that power to generate the Citadel’s many defensive void shields. Also forming part of this underground city was the central armoury. Here, for thousands of years, military stores of all kinds had been racked up. There were vehicles and weaponry there that not seen a battlefield in millennia. Many had been pressed back into service as the war closed in around the Citadel, such as the Malcadors and rarer still the Valdor tank hunters. The tank hunter were ancient vehicles equipped with the powerful but dangerous neutron laser- a weapon of advanced technology now lost to the Adeptus Mechanics. The upper levels had been turned into gigantic barracks and personnel shelters from the incessant shelling and air raids, as well as huge medical facilities and laboratories which had been put to heinous use.Thousands upon thousands of Krieg engineers now set about the task clearing the Citadel’s undercrofts. Corridor-by-corridor, chamber by chamber they fought with grenade and shotgun. The enemy had turned the depths of the Citadel into a vision of hell, setting loose all manner of twisted mutated creatures; some once human, others far less so; spawn that crawled and slithered, mutants that howled and screamed, warp-beasts and the hounds of Xaphan. They had once been guard dogs, great mastiffs commonly used by the garrison to keep rowdy a rebellious work gangs in order. There had been hundreds on Vraks but were now no longer recognizable as such. They had been used as hosts for the possession of ravenous daemon-spirits, and now they were massive blood-thirsty dog-creatures with huge fangs and claws that lived only to taste mortal blood. So large were they that only an Ogryn’s brute strength restrain them. Now the daemon-dogs stalked and hunted through the corridors of the undercroft, their howls a tortured baying that froze the blood.The Krieg engineers had to face such reckless and uncaring foes at every corner and in every chamber. Progress was slow, and the dark, dripping corridors became a charnel pit of corpses, friend and foe alike, Hundreds died on the first day and the engineers had only gained a small foothold on the lowest levels. More squads followed the first into the hell-hole, and more men died screaming on the fangs and claws of the warp-spawned beasts. The engineers fought back, using their poison gas grenades to clear rooms. In the darkness the fighting was grueling, but by sheer weight of numbers and bitter determination the Krieg engineers pushed onwards and upwards toward the surface. It would take weeks of fighting.