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. It remains a prominent blue-water navy with the ability to project power globally.^{[citation needed]}

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.