The base plays host to a large part of the surface fleet of the Royal Navy including the , the Type 45 destroyers, six Type 23 frigates, the River-class patrol vessels and a squadron of mine counter-measures vessels, both minesweepers and minehunters. Most of the vessels based in Portsmouth form part of the Portsmouth Flotilla, under the Fleet First reorganisation which saw the three port flotilla, Portsmouth, Devonport and Faslane, replace the frigate and destroyer squadrons and other groupings. The flotilla is a component unit of the Royal Navy Surface Fleet.