The Chapter Keep is the Grey Knights' fortress-monastery on the world — a bastion of blessed stone and ancient reliquaries, the source of the brotherhood's veteran reinforcement and its fortress income. It represents the order's home base as a controlled territory.
A gang that holds the Chapter Keep may, between battles, requisition a full Strike Brother or Brotherhood Terminator into its roster at the standard cost — never a recruit — and draws a fortress income each campaign turn. The reinforcements the Keep provides are always tested veterans, sanctioned and sealed, for the order makes no Juves and never will. It is a territory boon and a strategic prize: hold the Keep and the brotherhood grows stronger and better supplied; lose it and the irreplaceable few must fight on with only what they have.