sea power enables a state to use the oceans for commerce and war, while denying these facilities to enemies or rivals and controlling neutral shipping. This has been true since early periods. Sea-battles such as Salamis (480 bc) and Mycale (479 bc) played a part in compelling the Persian king Xerxes to abandon his invasion of Greece. During the struggle between Carthage and Rome for control of the western Mediterranean, fleet engagements at Mylae (260 bc), Cape Ecnomus (256 bc), and the Aegates Islands (241 bc) were equally decisive. The defeat of Marcus Antonius at the naval battle of Actium (31 bc) established the Julio-Claudian imperial dynasty of Rome. Two invasions of Japan launched by the Chinese Mongol emperor Kublai Khan in 1274 and 1281 were disastrous failures because of terrible losses inflicted on their fleets by storms. In 1571, the Christian victory at Lepanto crippled Ottoman naval power in the eastern Mediterranean and delivered a decisive check to Muslim western expansion. Successive Spanish armadas against the protestant English and Dutch, including major efforts in 1588 and 1639, failed because the attackers were unable to win command of the sea. Three hard-fought naval wars between Britain and the Dutch, in 1652–4, 1665–7, and 1672–4, were caused by commercial competition and rival claims to sea power. The victories of the British and Dutch fleets, now in alliance, at Barfleur and La Hogue in 1692 safeguarded the Glorious Revolution of 1688 against a Stuart restoration backed by France. The 18th cent. saw a series of wars in which sea power was crucial, in a world in which sea-borne commerce and overseas empires had expanded markedly. The French Revolutionary and Napoleonic wars (1793–1815) saw the culmination of naval warfare in the age of the sailing warship. Nelson's victory at the Nile in 1798 established British control of the Mediterranean, and Trafalgar on 21 October 1805 set the seal on British naval superiority. During the 19th cent., Britain's naval predominance sustained her world-wide commercial and imperial power, despite revolutions in warship design, including steam propulsion and protective armour.

The late 19th cent. saw increased scholarly analysis of the nature of sea power. Foremost was the American naval officer A. T. Mahan. He sought to explain Britain's success in attaining maritime hegemony, stressing that command of the sea in war could only be attained by the destruction or neutralizing of the enemy fleet. His first book, The Influence of Sea Power in History, 1660–1783 (1890), was particularly influential.

By 1914, while the heavily armed and armoured battleship was still seen as the principal naval weapon, the introduction of torpedoes and submarines had already necessitated protective screens for major warships. In the 1914–18 conflict allied sea power facilitated the dismemberment of Germany's overseas empire and enforced a blockade of Germany and Austria-Hungary. In both the First and Second World Wars, Germany's unrestricted submarine warfare at times seemed potentially decisive. Britain's dependence on overseas trade made her particularly vulnerable, though the introduction of the convoy system reduced losses and the allied navies eventually triumphed.

During the Second World War, advances in naval aviation introduced a further element into the struggle for naval supremacy. The Italian battle fleet, at anchor in its Taranto base, was badly damaged by a tiny force of obsolescent Fleet Air Arm aircraft in a raid in November 1940. In December 1941, planes from a Japanese carrier force crippled the American Pacific battle fleet at anchor at Pearl Harbor, though fortunately the American aircraft carriers were away at sea. Japanese sea power was vital in the allied defeats in the Far East in early 1942, but the survival of the American carriers brought a major Japanese defeat in the battle of Midway in June 1942. The principal Japanese striking force suffered disastrous losses in an engagement in which the main warships involved never saw each other, strikes by carrier aircraft proving decisive. Sea power was important in the European theatre of war, in the battle of the Atlantic, and in the north African campaigns, but its most convincing demonstration was in the allied advance in the Pacific between 1942 and 1945. ‘Island-hopping’ campaigns, moving ever closer to the Japanese home islands, were made possible by the development of forces capable of keeping the sea for long periods, backed by a sea-borne supply system. Before the atomic bomb brought Japan to surrender, her defeat had been ensured by the success of American submarines and aircraft in decimating Japanese shipping, depriving the Japanese war machine of oil and other vital raw materials. Since the 1960s, the submarine armed with nuclear missiles has become the single most potent embodiment of sea power.

Norman McCord

Sea Power. See Mahan, Alfred T.; Strategy: Naval Warfare Strategy.