These words all refer to organized groups of vessels. Fleet may refer to the entire number of ships of a nation, including merchant vessels, whereas navy refers either to the warships of a country or to its entire military sea force, including servicemen, depots and equipment. Navy always implies a military purpose, whereas fleet need not. Fleet is used, however, to mean all the ships under one command in a particular area, and the command may be a military one.

• The U.S. Sixth Fleet was assigned to the war in South-East Asia; a Russian fishing fleet of trawlers.

Fleet is also commonly used to refer to a group of vessels or vehicles organized or viewed as a unit, or belonging to one company: a fleet of taxis.

• A fleet of buses brought the club members and their families to the picnic ground; The company’s fleet of tugboats was laid up by the strike.

Armada , the Spanish word for armed, means a fleet of warships. The word is commonly associated with the disastrous experience of the Spanish (or Invincible) Armada , which sailed against England in 1588, was defeated, and was virtually destroyed by storms.

A convoy usually refers either to the protecting escort accompanying ships at sea, as in dangerous areas during wartime, or to the ships being so escorted. The word need not be restricted to ships, however; trains or trucks may also be considered convoys . Convoy is also applied to a group of military vehicles, such as trucks, personnel carriers, tanks, mounted guns, etc., travelling together in an organized way for protection, efficient movement, or to avoid impeding other traffic.