A navy is a military organisation that primarily operates in sea-based war.
Most (but not all) armed forces make considerable organisational distinction
between the land-based warfare of an Army, the sea-based warfare of a
Navy, and the air-based warfare of an Air Force - often splitting the three components into mostly independent forces.
A modern navy typically uses a combination of ships, boats, submarines, and aircraft
launched from aircraft carriers.
Many navies include ground forces (marines) to fight on land
and defend sea craft.
In many countries, the navy is the oldest branch of the armed services. Hence, for example, the British term "the Senior Service".
See also Naval warfare tactics, sea power[?].
Merchant navy is a British and Commonwealth term for the civilian seafaring industry, recognizing both the shared hazards of seafaring activity during wartime, as well as the expectation that civilian vessels may be put under various kinds of control by military authorities. In the USA the equivalent term is merchant marine.
For a list of the prefixes used with ship names (HMS, USS, &c.) see ship prefix.
