The quantity of ships in active service are categorized as follows: * A/C carriers: Aircraft carriers are major vessels designed to carry aircraft and helicopters. Amphibious assault ships are not included. * Major surface: Frigates, Destroyers and Cruisers of more than 1,000 tons displacement * Minor surface: Patrol boats and attack craft of less than 1,000 tons displacement * Submarines: All submarines * Mine warfare: Ships with primary roles of minelaying, hunting, and sweeping * Amphibious: Ships designed for landing troops and equipment and supporting amphibious operations * Logistical: Transports, tenders, tankers, and other support vessels and service craft * Other ships: Any ships not within the above groups