Killing Ground

'Regiments that have served for more than ten years are usually transferred from protracted war zones into armies of conquest. Not only are these the best troops, but they are also the oldest, having fought gallantly for the Emperor for a decade or more. Their reward is to take part in the conquest of a new world. If they are successful the entire regiment earns the highest honour the Imperium can bestow, the gratitude of the Emperor and the right to settle a new planet. All over the Imperium there are worlds that were originally populated in this way. Their people are the hardy descendants of victorious Imperial Guard regiments.'

Tactica Imperium - Commanders' notes on protracted service.