<P> Most military submarines are either attack submarines or ballistic missile submarines . Until the end of World War II the primary role of the diesel / electric submarine was anti-ship warfare, inserting and removing covert agents and military forces, and intelligence - gathering . With the development of the homing torpedo, better sonar systems, and nuclear propulsion, submarines also became able to effectively hunt each other . The development of submarine - launched nuclear and cruise missiles gave submarines a substantial and long - ranged ability to attack both land and sea targets with a variety of weapons ranging from cluster munitions to nuclear weapons . </P> <P> Most navies also include many types of support and auxiliary vessel, such as minesweepers, patrol boats, offshore patrol vessels, replenishment ships, and hospital ships which are designated medical treatment facilities . </P> <P> Fast combat vessels such as cruisers and destroyers usually have fine hulls to maximize speed and maneuverability . They also usually have advanced marine electronics and communication systems, as well as weapons . </P> <P> Some components exist in vessels of any size and purpose . Every vessel has a hull of sorts . Every vessel has some sort of propulsion, whether it's a pole, an ox, or a nuclear reactor . Most vessels have some sort of steering system . Other characteristics are common, but not as universal, such as compartments, holds, a superstructure, and equipment such as anchors and winches . </P>

When does a ship ceases to be called ship