Titanicus - Dan Abnett

When the world of Orestes comes under attack by a force of Chaos Titans, the Imperial Titans of Legio Invicta stride out in defence of the vital forge world.

Fresh from a hard-fought military campaign, one of the Imperium's most celebrated Titan Legions, the Legio Invicta, prepares to ship out to the warzones of the Sabbat Worlds. However, while stopping at the forge world of Orestes for refit and repair, the Legio Invicta finds itself thrown back into battle when a force of Chaos Titans attacks. But as the god-machines of the Adeptus Titanicus stride to war, a sudden religious schism threatens to tear the Adeptus Mechanicus apart and destroy the very world they have pledged to protect, testing the resolve of the Imperial defenders to the limit.