A navy is the branch of a nation's armed forces principally designated for naval warfare and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions. It includes anything conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields; recent developments have included space related operations. The strategic offensive role of a navy is projection of force into areas beyond a country's shores (for example, to protect sea-lanes, ferry troops, or attack other navies, ports, or shore installations). The strategic defensive purpose of a navy is to frustrate seaborne projection-of-force by enemies. The strategic task of the navy also may incorporate nuclear deterrence by use of nuclear missiles.
An occurrence of a 5 country multinational fleet, during Operation Enduring Freedom in the Oman Sea. In four descending columns, from left to right: ITS Maestrale, De Grasse; USS John C. Stennis, Charles De Gaulle, Surcouf; USS Port Royal, HMS Ocean, USS John F. Kennedy, HNLMS Van Amstel; and ITS Luigi Durand de la Penne. Source: Wikipedia