A navy is a military organisation that operates primarily on the sea.
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.
Merchant navy is a British and Commonwealth term for the civilianseafaring 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.
