Navy, seaborne armed force maintained for national defense or attack. In ancient times, Greek and Roman ships ruled the Mediterranean. In Scandinavia the Vikings ravaged the coasts of Europe from c.A.D. 800 for over 200 years. By the later 16th century most western European nations had acquired naval forces. Spain emerged as the leading naval power, but after its Armada was defeated by the English in 1588, England had mastery of the seas. England's naval supremacy was challenged by Holland and France, but the Battle of Trafalgar in 1805 restored it for another 100 years. The submarine and the aircraft carrier have replaced armored battleships. In the post-World War II period, Britain was overshadowed as a leading naval power by the United States and the former USSR.