The were second tier naval bases, similar to the first tier , with docking, fueling and resupply facilities, but typically lacked a shipyard or training school. They tended to be established by strategic waterways or major port cities for defensive purposes. In concept, the Guard District was similar to the United States Navy Sea Frontiers concept. the Guard District maintained a small garrison force of ships and Naval Land Forces which reported directly to the Guard District commander, and hosted detachments of the on a temporary assignment basis.