The Royal Navy (RN) is the naval warfare service branch of the British Armed Forces. Tracing its origins to the 16th century, it is the oldest service branch and is known as the Senior Service. From the end of the 17th century until well into the 20th century it was the most powerful navy in the world, playing a key part in establishing the British Empire as the dominant world power.

Following victory in the First World War the Royal Navy was significantly reduced in size, although at the onset of the Second World War it was still the largest in the world. By the end of the Second World War the U.S. Navy had emerged as the world's largest. During the course of the Cold War and the emergence of the Soviet submarine threat, the Royal Navy transformed into a primarily anti-submarine force, hunting for Soviet submarines, mostly active in the GIUK gap. Following the collapse of the Soviet Union its focus has returned to global expeditionary operations.

The Royal Navy operates a fleet of technologically sophisticated ships including an aircraft carrier (though without any fixed-wing aircraft), a helicopter carrier, two landing platform docks, four ballistic missile submarines (which maintain the UK's nuclear deterrent), seven nuclear fleet submarines, six guided missile destroyers, 13 frigates, 15 mine-countermeasure vessels and 24 patrol vessels. As of April 2012, there were 79 commissioned ships in the Royal Navy, plus 19 commissioned ships of the Royal Fleet Auxiliary (RFA) which also contribute to the Royal Navy's available sea-going assets. The RFA primarily serves to replenish Royal Navy warships at sea, and also augments the Royal Navy's amphibious warfare capabilities through its three Bay-class landing ship dock vessels.