Careers in this field focus on the safe operation of marine vessels or watercraft in executing military missions. The Military has the most technically and tactically advanced defense and war-fighting capabilities to uphold national security at and under, the sea with its vast fleet of aircraft carriers, cruisers, destroyers, frigates, dock landing ships, cutters, other surface vessels and submarines. The officers and crew on these vessels are responsible for ensuring that they can safely and successfully complete their missions.