Editing Underworld War (section)

==Preliminaries==

By the final stages of the Battle of Calth, the planet was suffering from the aftereffects of the Word Bearers' bombardment and the radiation flares emanating from the poisoned star of Veridia. Recognizing that the planet's surface was shortly going to become uninhabitable, Captain Remus Ventanus of the 4th Company issued a general order to all remaining loyalists on the planet: they were to move immediately to the nearest arcology or cave system to take shelter until the radiation storms dissipated or the Ultramarines fleet was able to return and extract them. There were approximately forty thousand Ultramarines still alive on Calth, all of whom obeyed this order, along with the surviving loyalist elements of the Imperial Army and Mechanicum and as many civilian survivors as could be rounded up. The Word Bearers and Chaos forces still alive on the surface had the same idea, and soon both sides were fighting over the available caves and arcologies.