Hull number is a serial identification number given to a boat

Boat

A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

 or ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

. A lower number implies an older vessel. The precise usage varies by country and type.

For civilian craft manufactured in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, the hull number is given to the vessel when it is built and forms part of the hull identification number, which uniquely identifies the vessel and must be permanently affixed to the hull in at least two places. A Hull Identification Number (HIN) is a unique set of 12 characters, similar to the Vehicle Identification Number

Vehicle identification number

A Vehicle Identification Number, commonly abbreviated to VIN, is a unique serial number used by the automotive industry to identify individual motor vehicles. VINs were first used in 1954...

 which is found on automobiles. The HIN may be found on the aft of the vessel in the uppermost right corner. Also, the HIN may be stated on the title, registration, and insurance documents.

The United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

, United States Coast Guard

United States Coast Guard

The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...

, and United States National Oceanic and Atmospheric Administration

National Oceanic and Atmospheric Administration

The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 employ hull numbers in conjunction with a hull classification symbol

Hull classification symbol

The United States Navy, United States Coast Guard, and United States National Oceanic and Atmospheric Administration use hull classification symbols to identify their ship types and each individual ship within each type...

 to uniquely identify vessels and to aid identification. A particular combination of hull classification and hull number is never reused and therefore provides a means to uniquely identify a particular ship. For example, there have been at least eight vessels named USS Enterprise

USS Enterprise

USS Enterprise may refer to the following vessels:-United States of America:In watercraft, the prefix "USS" or "U.S.S." is applied to ships commissioned by and for the United States Navy. Private citizens also use the name unofficially...

, but CV-6 uniquely identifies the World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 carrier from all others.

The U.S. Navy sometimes ignores the sequence of hull numbering. For example, the Navy built the last Los Angeles-class submarine

Los Angeles class submarine

The Los Angeles class, sometimes called the LA class or the 688 class, is a class of nuclear-powered fast attack submarines that forms the backbone of the United States submarine fleet. With 43 submarines on active duty and 19 retired, the Los Angeles class is the most numerous nuclear powered...

 as SSN-773

USS Cheyenne (SSN-773)

USS Cheyenne , the last , is the third ship of the United States Navy to be named for Cheyenne, Wyoming. The contract to build her was awarded to Newport News Shipbuilding and Dry Dock Company in Newport News, Virginia on 28 November 1989 and her keel was laid down on 6 July 1992. She was launched...

; then built SSN-21 through SSN-23

Seawolf class submarine

The Seawolf class is a class of nuclear-powered fast attack submarines in service with the United States Navy. The class was the intended successor to the , ordered at the end of the Cold War in 1989. At one time, an intended fleet of 29 submarines was to be built over a ten-year period, later...

; and later resumed the original sequence with SSN-774

USS Virginia (SSN-774)

USS Virginia is a United States Navy attack submarine, the lead boat of her class and the tenth vessel of the Navy to be named for the Commonwealth of Virginia....

 for the next class of submarines. This was done because the Seawolfs were to be a radical new design for the endgame of the Cold War

Cold War

The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

, but severe cost overruns combined with the downsizing of the defense budget and the end of the Cold War resulted in only the three boats being constructed.

When a naval vessel is refitted for use as a different type of ship, a new hull number is sometimes assigned along with its new classification. Often the number remains the same while the hull classification changes. For convenience, the combined designation, which is painted on the side of the ship, is frequently called the hull number.

Hull numbers are also used to identify tank

Tank

A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

s.