The Royal Navy (RN) is the United Kingdom's naval warfare force and a component of His Majesty's Naval Service. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against France. The modern Royal Navy traces its origins to the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.
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 until the Second World War, it was the world's most powerful navy. The Royal Navy played a key part in establishing and defending the British Empire, and four Imperial fortress colonies and a string of imperial bases and coaling stations secured the Royal Navy's ability to assert naval superiority globally. Owing to this historical prominence, it is common, even among non-Britons, to refer to it as "the Royal Navy" without qualification. Following World War I, it 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, hunting for Soviet submarines and mostly active in the GIUK gap. Following the collapse of the Soviet Union, its focus has returned to expeditionary operations around the world and it remains one of the world's foremost blue-water navies.
The Royal Navy maintains a fleet of technologically sophisticated ships, submarines, and aircraft, including 2 aircraft carriers, 2 amphibious transport docks, 4 ballistic missile submarines (which maintain the nuclear deterrent), 6 nuclear fleet submarines, 6 guided missile destroyers, 11 frigates, 9 mine-countermeasure vessels and 26 patrol vessels. As of April 2023, there are 70 operational commissioned ships (including submarines as well as one historic ship, ) in the Royal Navy, plus 13 ships of the Royal Fleet Auxiliary (RFA); there are also five Merchant Navy ships available to the RFA under a private finance initiative.