Ships

Historically, navy ships were primarily intended for warfare. They were designed to withstand damage and to inflict the same, but only carried munitions and supplies for the voyage (rather than merchant cargo). Often, other ships which were not built specifically for warfare, such as the galleon or the armed merchant ships in World War II, did carry armaments. In more recent times, navy ships have become more specialized and have included supply ships, troop transports, repair ships, oil tankers and other logistics support ships as well as combat ships. So long as they are commissioned, however, they are all "ships".

Modern navy combat ships are generally divided into seven main categories: aircraft carriers, cruisers, destroyers, frigates, corvettes, submarines, and amphibious assault ships. There are also support and auxiliary ships, including the oiler, minesweeper, patrol boat, hydrographic and oceanographic survey ship and tender. During the age of sail, the ship categories were divided into the ship of the line, frigate, and sloop-of-war.

Naval ship names are typically prefixed by an abbreviation indicating the national navy in which they serve. For a list of the prefixes used with ship names (HMS, USS, etc.) see ship prefix.

Today ships are significantly faster than in former times, thanks to much improved propulsion systems. Also, the efficiency of the engines has improved, in terms of fuel, and of how many sailors it takes to operate them. In World War II, ships needed to refuel very often. However, today ships can go on very long journeys without refueling. Also, in World War II, the engine room needed about a dozen sailors to work the many engines, however, today, only about 4–5 are needed (depending on the class of the ship). Today, naval strike groups on longer missions are always followed by a range of support and replenishment ships supplying them with anything from fuel and munitions, to medical treatment and postal services. This allows strike groups and combat ships to remain at sea for several months at a time.

Boats

Many people make the mistake of calling a ship a "boat". The term "boat" refers to small craft limited in their use by size and usually not capable of making independent voyages of any length on the high seas. The old navy adage to differentiate between ships and boats is that boats are capable of being carried by ships. (Submarines by this rule are ships rather than boats, but are customarily referred to as boats reflecting their previous smaller size.) Navies use many types of boat, ranging from 9-foot (2.7 m) dinghies to 135-foot (41 m) landing craft. They are powered by either diesels, out-board gasoline motors, or waterjets. Most boats are built of aluminum, fiberglass, or steel.

Standard Boats A standard boat is a small craft carried aboard a ship to perform various tasks and evolutions.

Landing Craft These boats, carried by various amphibious ships, are designed to carry troops, vehicles, or cargo from ship to shore under combat conditions, to unload, to retract from beach, and to return to the ship. They are especially rugged, with powerful engines, and they are armed. They are usually referred to by their designations such as LCPL (landing craft, personnel) LCM (landing craft mechanized) or LCU (landing craft, utility) rather than by full name. There are many types in todays navies. They will typically have a power operated bow ramp, a cargo well and after structures that house enginerooms, pilot houses, and stowage compartments.

Landing Craft, Air Cushioned Known as LCAC also most commonly called a hover craft. Floats on a cushion of air that allows travel over water and land. It can deliver troops, equipment, and supplies. Examples of these include the Zubr and the Textron LCAC.

Rigid hull Inflatable Boats Generally known as RIBs these are versatile boats designed for service as a standard ship's boat. The distinguishing feature is a hull formed from a combination of a rigid planing hull with an inflatable tube. They range in length from 2.5 and 18 metres (7.5 and 55 ft).

Personnel Boats (PE) These are fast, V bottomed, diesel powered boats with enclosed spaces specifically designed to transport officers, although smaller types are used for shore party boats, lifeboats, and mail boats. They may be known as launches, gigs or barges depending on the type of personnel they carry.

Utility Boats These boats, varying in length from 18 feet (5.5 m) to 15 meters (50 ft) are mainly cargo and personnel carrier or heavy duty work boats. Many have been modified for survey work, tending divers, and minesweeping operations. In ideal weather, a 15-meter (50 ft) UB will carry 146 people, plus crew. Utility boats are open boats, though many of the larger ones are provided with canvas canopies. The smaller utility boats are powered by outboard engines. The larger boats have diesel engines.

Punts These are open square enders, 14 feet (4.3 m) long. They are either rowed or sculled, and are generally used in port by side cleaners.

Special Boats These boats, used by shore stations and for special missions, are not normally carried aboard ships as are the standard boats discussed above. They include line handling boats, buoy boats, aircraft rescue boats, torpedo retrievers, explosive ordnance disposal craft, utility boats, dive boats, targets, and various patrol boats. Many standard boats have been modified for special service.

Mark V Special operations craft (SOC) This craft is also used for insertion and extraction of special warfare personnel. The craft is 82 feet (25 m) long, and has twain diesel engines driving waterjets. The craft is capable of speeds in excess of 50 knots (93 km/h) and is air deployable.

Patrol Boats, River (PBR) This is a 31-foot (9.4 m), 25 knots (46 km/h), twin diesel boats with a fiberglass hull and waterjet pump propulsion that permits it to operate in 15 inches (380 mm) of water. The PBR is highly maneuverable and can reverse course in its own length. It carries radar, communications equipment, and machine guns

Navy Units

Naval forces are typically arranged into units based on the number of ships included, a single ship being the smallest operational unit. Ships may be combined into squadrons or flotillas, which may be formed into fleets. The largest unit size may be the whole Navy or Admiralty.

Navy Ranks

A navy will typically have two sets of ranks, one for enlisted personnel and one for officers.

Typical ranks for commissioned officers include the following, in ascending order (Commonwealth ranks are listed first on each line; USA ranks are listed second in those instances where they differ from Commonwealth ranks):

• Acting Sub-Lieutenant / Ensign / Corvette Lieutenant
• Sub Lieutenant / Lieutenant Junior Grade / Frigate Lieutenant
• Lieutenant (Commonwealth & USA)/ Ship-of-the-Line Lieutenant / Captain Lieutenant
• Lieutenant Commander (Commonwealth & USA)/ Corvette Captain
• Commander (Commonwealth & USA)/ Frigate Captain
• Captain (Commonwealth & USA)/ Ship-of-the-Line Captain
• Commodore / Flotilla Admiral (in USA only: Rear Admiral (lower half))
• Rear Admiral (in USA only: Rear Admiral (upper half))
• Vice Admiral (Commonwealth & USA)
• Admiral (Commonwealth & USA)
• Fleet Admiral (USA) or Admiral of the Fleet (Commonwealth) or Grand Admiral

"Flag officers" include any rank that includes the word "admiral" (or commodore in services other than the US Navy), and are generally in command of a battle group, strike group or similar flotilla of ships, rather than a single ship or aspect of a ship. However, commodores can also be temporary or honorary positions. For example, during World War II, a Navy captain was assigned duty as a convoy commodore, which meant that he was still a captain, but in charge of all the merchant vessels in the convoy. Today, the U.S. Navy uses the term "commodore" for captains in command of multiple vessels (destroyer squadrons, submarine squadrons, riverine squadron), multiple aviation squadrons (air wing or air group) or other units (i.e., special warfare group, etc.). The exception to this rule is carrier air wing commanders who are known as "CAG" from their former title as Commander, Carrier Air Group.

The most senior rank employed by a navy will tend to vary depending on the size of the navy and whether it is wartime or peacetime, for example, few people have ever held the rank of Fleet Admiral in the U.S. Navy, the chief of the Royal Australian Navy holds the rank of Vice Admiral, and the chief of the Irish Naval Service holds the rank of Commodore.

Coast Guards will typically employ naval ranks. For example, the U.S. Coast Guard uses the same officer rank titles as the U.S. Navy with the exception of Fleet Admiral.