His Majesty's Naval Service in the context of "Serco Marine Services"

The Royal Navy (RN) is the naval warfare force of the United Kingdom, responsible for defending the UK, the Crown Dependencies, and the Overseas Territories from naval attack or invasion. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King. 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 English Navy of the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.

From the early 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. Following World War I, it was significantly reduced in size. 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 returned to expeditionary operations.

The Royal Navy (RN) is the naval warfare force of the United Kingdom, responsible for defending the UK, the Crown Dependencies, and the Overseas Territories from naval attack or invasion. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King. 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 English Navy of the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.

From the early 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. Following World War I, it was significantly reduced in size. 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 returned to expeditionary operations. Following a projected £2 billion overspend acknowledged by the MOD in 2025, the Royal Navy announced it will reduce overseas training in the Indo-Pacific and the Middle East.

The Navy Department was a former ministerial service department of the British Ministry of Defence responsible for the control and direction of His Majesty's Naval Service. It was established on 1 April 1964 when the Admiralty was absorbed into a unified Ministry of Defence, where it became the Navy Department. Political oversight of the department originally lay with the Minister of Defence for the Royal Navy (1964–1967) it then passed to the Parliamentary Under-Secretary of State for Defence for the Royal Navy (1967–1981), then later to the Parliamentary Under-Secretary of State for the Armed Forces (1981–1990), and finally the Parliamentary Under-Secretary of State for Defence (1991–1997).

The department's military head was the First Sea Lord and Chief of Naval Staff (1964–1997), who was responsible for managing the day-to-day operations of the department. Following restructuring in 1997, the individual Navy Department was abolished and its functions were transferred to the new Royal Navy (now Navy) operational branch of the Ministry of Defence.

First Sea Lord, officially First Sea Lord and Chief of the Naval Staff (1SL/CNS), is a statutory position in the British Armed Forces, held by an admiral or a general of His Majesty's Naval Service. As the highest-ranking officer in the Naval Service, the chief is the principal military advisor on matters pertaining to the navy and a deputy to the Secretary of State for Defence. The CNS is also a member of the Chiefs of Staff Committee and, thereby, a military advisor to the National Security Council, the prime minister and the monarch. The First Sea Lord is typically the highest-ranking officer on active duty of the Royal Navy unless the Chief of the Defence Staff is a naval officer. The post is currently held by General Sir Gwyn Jenkins.

Originally titled the "Senior Naval Lord to the Board of Admiralty" when the post was created in 1689, the office was re-styled First Naval Lord in 1771. The concept of a professional "First Naval Lord" was introduced in 1805, and the title of the office was changed to First Sea Lord on the appointment of Sir John "Jackie" Fisher in 1904. Since 1923, the First Sea Lord has been a member of the Chiefs of Staff Committee; they now sit on the Defence Council and the Admiralty Board.

The Royal Fleet Auxiliary (RFA) is a naval auxiliary fleet owned by the UK's Ministry of Defence. It is a component of His Majesty's Naval Service and provides logistical and operational support to the Royal Navy and Royal Marines.

The RFA ensures the Royal Navy is supplied and supported by providing fuel and stores through replenishment at sea, transporting Royal Marines and British Army personnel, providing medical care and transporting equipment and essentials around the world. In addition the RFA acts independently providing humanitarian aid, counter piracy and counter narcotic patrols together with assisting the Royal Navy in preventing conflict and securing international trade. They are a uniformed civilian branch of the Royal Navy staffed by British merchant sailors.

The Navy Board is the body responsible for the day-to-day running of His Majesty's Naval Service. Its composition is similar to that of the Admiralty Board of the Defence Council of the United Kingdom, except that it does not include any of His Majesty's Ministers. The Board shares a name with its historic predecessor, the Navy Board of 1546 to 1832, but is unrelated in structure or membership.