A navy is a military organization with the principal mission of fighting from, above, or under water. Some of the basic naval missions go back to antiquity, while others, such as ballistic missile defense, are recent.
Navies vary in their geographic scope, the types of warfare missions they can conduct, and the types of ships and weapons they employ; see Navy/Related Articles for a detailed list.
Navies may be limited to the "brown water" of rivers and near the shore, the "green water" of the littoral including straits and confined international waters, and the "blue water" of the open ocean. The ability to operate in polar regions, including under the ice, is a special capability.
Power projection tends to imply blue-water capability. Relatively few navies can put a combat fleet anywhere in the world. Even with the great tradition of the Royal Navy, the 1982 Falklands War was a surprise when Britain fought the largest naval and amphibious operation in recent history, thousands of miles from home.
Littoral warfare is receiving the greatest attention today. Many techniques refined for blue-water operations in the Cold War are obsolescent; the North Atlantic is not likely to be a battle area. The Persian Gulf, Gulf of Aden, Strait of Malacca, and other confined waters are of critical interest.
Another reason for interest in the littoral is what the United States Navy calls its "from the sea" doctrine. Forces, including land forces delivered by amphibious warfare or aircraft and missiles operating from ships, do not need land bases and the associated complex diplomacy.
The United States Navy is, by far, the world's largest and most capable. While much smaller, the British Royal Navy consistently demonstrates excellent capabilities. With much smaller budgets than during the Soviet period, the training and maintenance of the Russian Federation Navy is uncertain. The French Navy is competent.
Some navies are expanding traditional roles. It is fairly clear that the Indian Navy is developing blue-water capability, at least in its region; it is second in opeational aircraft carriers, a measure of power projection, to the U.S. Navy. China's Peoples' Liberation Army Navy is developing more cautiously, experimenting with carriers but still basically a green-water force.
Within its region, the Japanese Maritime Self-Defense Force is quite capable, although under significant political and legal restrictions on taking aggressive action; it is deliberately not called a navy. Nevertheless, it has first-rate combatants, capable of ballistic missile defense and anti-submarine warfare, as a check on North Korea and China.
At its most basic, naval warfare takes place on, above, and below the surface of the water, as well as at the meeting of land and sea. Anti-surface warfare is the classic ship-to-ship mission, which can involve freedom of navigation and sea control as well as direct combat. Amphibious warfare starts from the surface although some air and underwater methods are used.
Mine warfare is just under the surface, although mines can be laid by aircraft, ships, and submarines.
Anti-submarine warfare, against both attack and missile submarines, involves surface, submarine, and aircraft platforms.