Royal Navy, naval military organization of the United Kingdom, charged with the national defense at sea, protection of shipping, and fulfillment of international military agreements.

Organized sea power was first used in England by Alfred the Great of Wessex, who launched ships to repel a Viking invasion. Naval activity continued to be local, defensive, and temporary until the 13th century, when Normandy was lost to France and trade was extended to Spain and Portugal. Ships were then used to transport soldiers to battles on land. In the Battle of Sluis (1340), however, the English naval force engaged in at-sea fighting.

Henry VIII built a fleet of fighting ships armed with large guns and created a naval administration. Under Elizabeth I the navy developed into England’s major defense and became the means by which the British Empire was extended around the globe. The maritime forces were given the name Royal Navy by Charles II, although the military forces had come under control of Parliament during the English Civil Wars (1642–51).

During the 18th century the Royal Navy engaged in a long struggle with the French navy for maritime supremacy, leading Britain to victory over France in four separate wars between 1688 and 1763. It played a key role in Britain’s stand against Napoleon, and, after winning the Battle of Trafalgar in 1805, the Royal Navy was never again challenged by the French. This same period saw, in the person of Lord Nelson, perhaps the greatest admiral in history. For the rest of the 19th century, the Royal Navy helped enforce what became known as the Pax Britannica—i.e., the long period of relative peace arising from a balance of power between the major European states that depended ultimately on the use of British maritime supremacy.

The Royal Navy continued to be the world’s most powerful navy well into the 20th century. During World War I its main mission was the protection of shipping from submarine attack. Naval aviation was established by the British during that war, and the Fleet Air Arm was given control of all ship-borne aircraft in 1937. After World War II the Royal Navy was second in size only to the U.S. Navy and continued to be a world leader in maritime, and especially antisubmarine, operations.

In 1964 the Board of Admiralty was brought into the Ministry of Defense. After 1967 naval administration was headed by an undersecretary of state for the navy. Royal Navy organization includes the Surface Fleet, the Submarine Service, the Fleet Air Arm, the Royal Marines, and the Royal Fleet Auxiliary. Although the Royal Navy has been reduced in size since the 1960s, it was given responsibility for nuclear deterrence in 1969 and maintains a fleet of nuclear-armed submarines. The Royal Navy played a critical role in the Falkland Islands War (1982), although that conflict demonstrated the toll that antiship missiles could take on surface craft. In the early 21st century the power of the Royal Navy had declined somewhat, but it still remained one of the world’s top four navies, after those of the United States, Russia, and China.