Titanicus

When the vital forge world of Orestes comes under attack by a legion of Chaos Titans, the planet is forced to appeal for help. The Titans of Legio Invicta, although fresh from combat and in desperate need of refit and repair, respond, committing their own force of war engines to the battle. As the god-machines stride to war, the world trembles, for the devastation they unleash could destroy the very world they have pledged to save.

Read it because

It's a vision of total war in the 41st millennium, from the smallest soldier to the largest God-Machine.