Warhammer 40k - Space Marine Battles Novella - Engines of War by Steve Lyons

The Ultramarines descend upon the plague-wracked world of Orath. Captain Galenus of the Fifth Company leads a force to wrest control of Fort Kerberos from the enemy. But with the dread forces of Chaos arrayed against them, it will take more than firepower for the Space Marines to defeat their rot-infested foes and save Orath from a grisly doom. As death comes from the ground and the air, Galenus and his warriors must be prepared to sacrifice all to achieve victory.