Electricity is stored in four lead-acid battery packs, totalling 400 tonnes, assembled by Pacific Marine Batteries, a joint venture between VARTA of Germany and Pacific Dunlop of Australia. These supply a single Jeumont Schneider DC motor, which provides 7,200 shaft horsepower to a seven-bladed, diameter skewback propeller. The propeller design is classified Top Secret, and must be covered before a "Collins"-class submarine can be removed from the water for maintenance. Emergency propulsion is provided by a MacTaggart Scott DM 43006 retractable hydraulic motor. The aft control surfaces are mounted on an X-shaped structure, giving the boats the ability to outmanoeuvre most warship and submarine classes.