Haradni 13th
The Haradni 13th, also known as the Haradni 13th Heavy Armour Regiment was a regiment of the Imperial Guard which at an unknown point defected to Chaos and joined the forces of Abaddon the Despoiler. During the 13th Black Crusade, the Haradni 13th would be charged with capturing Medusa, homeworld of the Iron Hands Space Marines. At their peak the Regiment is said to have fielded over 10,000 tanks, including not only Leman Russ Battle Tanks but also heavier Super heavy tanks such as Baneblades. In the end however they were defeated in the largest armoured battle of the Imperium since the Horus Heresy and wiped out by the Iron Hands and their PDF forces.[1]