Definitions, Tonnages and Equivalents

ACTIVE - Ships currently in use or in an operating/readiness status.

BALE CUBE - The space available for cargo measured in cubic feet to the inside of the cargo battens, on the frames, and to the underside of the beams.

BARREL - 42 gallons, 5.615 cubic feet in volume.

CALL SIGN - International Radio Call Sign (IRCS).

CARGO DEADWEIGHT - Capacity is determined by deducting from total deadweight the weight of fuel, water, stores, dunnage, crew passengers, and other items necessary for use on a voyage.

DEADWEIGHT - The total lifting capacity of a ship expressed in tons of 2240 lbs. It is the difference between the displacement light and the displacement loaded.

DISPLACEMENT, LIGHT - The weight of the ship excluding cargo, fuel, ballast, stores, passengers, crew, but with water in boilers to steaming level. Displayed by default.

DISPLACEMENT, LOADED - The weight of the ship including cargo, passengers, fuel, water, stores, dunnage and such other items necessary for use on a voyage, which brings the ship down to her load draft.

FOS - Full Operating Status. Ships are fully operational, with complete crews aboard. Ships are FOS after they have been fully activated.

GRAIN CUBE - The maximum space available for cargo measured in cubic feet, the measurement being taken to the inside of the shell plating of the ship or to the outside of the frames and to the top of the beam or underside of the deck plating.

*GROSS TONNAGE - The entire internal cubic capacity of the ship expressed in tons of 100 cubic feet to the ton, except certain spaces which are exempted, such as: (1) peak and other tanks for water ballast; (2) spaces above the uppermost continuous deck, such as: open forecastle, bridge and poop, certain light and air spaces, domes of skylights, condenser, anchor gear, steering gear, wheel house, galley and cabins for passengers.

INACTIVE - Ships identified are laid-up (non-operating/non-readiness status). The Reserve Fleet Inactive Summary includes ships under Headings for Title XI, MARAD and Navy.

LONG TONS - One long ton is equal to 2,240 pounds; used to measure petroleum products.

LONG TON MILES - One long ton transported one mile.

MEASUREMENT TON - Bale cubic in units of 40 cubic feet to the ton. A capacity of 10,000 M/T is the same as 400,000 cubic feet.

MEASUREMENT TON MILES - One measurement ton transported one mile.

*NET TONNAGE - The tonnage most frequently used for the calculation of tonnage taxes and the assessment of charges for wharfage and other port dues. Net tonnage is obtained by deducting from the gross tonnage, crew and navigating spaces and an allowance for the space occupied by the propelling machinery.

ROS - Reduced Operating Status. Ships in ROS have a small crew onboard to assure the readiness of propulsion and other primary systems if the need arises to activate the ship.

WEIGHT TON - Calculated as long ton (2,240 lbs.) Abbreviated W/T.

* Also referred to as Gross Register and Net Register Tonnage

Classifications/Prefixs Used in the Ship Inventory

Note: MSC ships carry the prefix "T" before their normal hull numbers. SECNAV Instruction 5030.8, dated 21 Nov 2006, provides classification for all naval ships and craft. Paragraph 3b, Special Instructions, states that "Letter prefixes shall be used in conjunction with classification symbols as follows: T -- To indicate that a government-owned or bareboat-chartered ship is assigned to Commander, Military Sealift Command (MSC) as a type commander."