The Royal Navy (RN) is the United Kingdom's naval warfare force. It is the oldest of the UK’s armed services and is sometimes known as the Senior Service. It was formally established as the national naval force of England in 1660, following the restoration of King Charles II to the throne. Warships were however used by the English kings from the early medieval period, with the first major maritime engagements fought in the Hundred Years' War against France.

From the middle decades of the 17th century, and through the 18th century, the Royal Navy vied with the Dutch Navy and later with the French Navy for maritime supremacy. From the mid 18th century, it was the world's most powerful navy until the Second World War. The Royal Navy played a key part in establishing the British Empire during the 19th and first part of the 20th centuries.

Following World War I, the Royal Navy was significantly reduced in size, although at the onset of World War II it was still the world's largest. During the Cold War, the Royal Navy transformed into a primarily anti-submarine force, Following the collapse of the Soviet Union, its focus has returned to expeditionary operations around the world. However, 21st-century reductions in naval spending have led to a personnel shortage and a reduction in the number of warships.

The Royal Navy is part of His Majesty's Naval Service, which also includes the Royal Marines. The professional head of the Naval Service is the First Sea Lord who is an admiral and member of the Defence Council of the United Kingdom. The Defence Council delegates management of the Naval Service to the Admiralty Board, chaired by the Secretary of State for Defence. The Royal Navy operates three bases in the United Kingdom where commissioned ships are based: Portsmouth, Clyde and Devonport, the last being the largest operational naval base in Western Europe.