On a Naval Ship or shore activity, a Department is a section devoted to one of several major tasks. Most Ships have Operations, Engineering, Deck or Weapons, and Medical Departments. Aircraft Carriers and some large landing vessels have an Aviation, while cargo ships have one for that purpose.

In the book Carrier , Tom Clancy records the various departments of the aircraft carrier USS George Washington as they were in autumn 1997.

• Administration (ADMIN)—the record keepers of the ship and oversees personnel, maintenance, logistics, financial and other records. The Officer in Charge (OiC) was a Lieutenant (O-3).
• Aircraft Maintenance Division (AIMD)—provides spares, maintenance facilities and support personnel for the Carrier Air Wing. The OiC was a Commander.
• Air Department (AIR)—oversees operations on the flight deck, hangers and air-space near the carrier. The OiC is known as the "Air Boss" and is a Commander; the 2iC is called the "Mini Boss" and is usually a Lieutenant Commander.
• Crew Recreation and Morale Department (CRMD)—looks after the crew's spiritual and moral welfare. The OiC was a Captain and the Command Chaplin of the ship.
• Deck Division (DECK)—handles lines, anchors and small boats among a range of other traditional sailor duties. The Deck Division is headed by a Lieutenant Commander.
• Dental Department (DENTAL)—provides dental services to the crew of the carrier and battle group. The OiC was a Commander.
• Engineering Department (CRMD)—responsible for most systems on board the ship from electrical power to sewage treatment. The Chief Engineer (CHENG) is usually a Lieutenant Commander. On non-nuclear ships the Engineering Department is responsible for the propulsion systems. On a nuclear-powered ship, the reactors are maintained by the secretive Reactor Department (REACTOR). The OiC of the reactors in the ship's Reactor Officer (RO) and is was a Captain.
• Combat Systems Division (CSD)—OiC: Combat System Officer (CSO)a CDR
• Legal Department (LEGAL)—OiC: Ship's Leagal Officer (LEGAL-OFF) an LCDR
• Medical Department (MEDICAL)—OiC: Ship's Medical Officer (SMO) a CDR
• Marine Detachment (MARDET)—OiC: Marine 1st Lieutenant
• Navigation Department (NAV)—OiC: Navigation Officer ('GATOR') a CDR
• Operations Department (OPS)—OiC: Operations Officer (OPSO) a CDR.
• Safety Department (SAFETY)—OiC: Safety Officer (SAFETYO) a CDR.
• Supply Department (SUPPLY)—OiC: Supply Officer (SUPPO) a CDR.
• Training Department (LEGAL)—OiC: an LT (O-3).
• Weapons Department (WEPS)— OiC: the 'Gunner' a CDR. Firing weapons controlled by the Tactical Officer (TACO) in the Combat Direction Centre (CDC).

See also: military science, Military History of the United States