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 minesweeper, patrol boat, 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 a lot, 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.