British Armed Forces

The British Armed Forces are the unified military forces responsible for the defence of the United Kingdom, its Overseas Territories and the Crown Dependencies. They also promote the UK's wider interests, support international peacekeeping efforts and provide humanitarian aid. The force is also known as His Majesty's Armed Forces.

Since the formation of the united Kingdom of Great Britain in 1707 (later succeeded by the United Kingdom of Great Britain and Ireland, and finally by the United Kingdom of Great Britain and Northern Ireland), the British Armed Forces have seen action in most major wars involving the world's great powers, including the Seven Years' War, the Napoleonic Wars, the Crimean War, the First World War and the Second World War. Britain's victories in most of these wars allowed it to influence world events and establish itself as one of the world's leading military and economic powers. The British Armed Forces consist of: the Royal Navy, a blue-water navy with a fleet of 62 commissioned and active ships, together with the Royal Marines, a highly specialised amphibious light infantry force; the British Army, the UK's principal land warfare branch; and the Royal Air Force, a technologically sophisticated air force with a diverse operational fleet consisting of both fixed-wing and rotary aircraft. The British Armed Forces include standing forces, Regular Reserve, Volunteer Reserves and Sponsored Reserves.

King Charles III, sovereign of the United Kingdom, is the commander-in-chief and is styled as Head of the Armed Forces, with officers and personnel swearing allegiance to him. Long-standing constitutional convention, however, has vested de facto executive authority, by the exercise of royal prerogative, in the Prime Minister and the secretary of state for defence. The Prime Minister (acting with the Cabinet) makes the key decisions on the use of the armed forces. The UK Parliament approves the continued existence of the British Army by passing an Armed Forces Act at least once every five years, as required by the Bill of Rights 1689. Only a "standing army" requires reapproval by Parliament; the Royal Navy, Royal Air Force and the Royal Marines and any other forces are not included in the requirement. The armed forces are managed by the Defence Council.

The United Kingdom is one of five recognised nuclear powers, a permanent member on the United Nations Security Council, a founding and leading member of NATO and party to the AUKUS security pact and the Five Power Defence Arrangements. Overseas garrisons and training facilities are maintained at Ascension Island, Bahrain, Belize, Bermuda, British Indian Ocean Territory, Brunei, Canada, Cyprus, the Falkland Islands, Germany, Gibraltar, Kenya, Montserrat, Nepal, Qatar, Singapore and the United States. The British Armed Forces provided military training to approximately 140 countries in 2024–25.

With the Acts of Union 1707, the armed forces of England and Scotland were merged into the armed forces of the Kingdom of Great Britain.

There were originally several naval and several military regular and reserve forces, although most of these were consolidated into the Royal Navy or the British Army during the 19th and 20th Centuries (the Royal Naval Air Service and the Royal Flying Corps of the British Army, by contrast, were separated from their parent forces in 1918 and amalgamated to form a new force, the Royal Air Force, which would have complete responsibility for naval, military and strategic aviation until the Second World War).

Naval forces included the Royal Navy, the Waterguard, later renamed the HM Coastguard, and Sea Fencibles and River Fencibles formed as and when required for the duration of emergencies. The Merchant Navy and offshore fishing boat crews were also important manpower reserves to the armed naval forces. Any seaman was liable to impressment, with many so conscripted especially during the two decades of conflict from the French Revolution until the end of the Napoleonic Wars, and from 1835 registered on the Register of Seamen to identify them as a potential resource, and many of their seamen would serve part time in the Royal Navy Reserve, created under the Naval Reserve Act 1859, and Royal Naval Volunteer Reserve, created in 1903.

The British military (those parts of the British Armed Forces tasked with land warfare, as opposed to the naval forces) historically was divided into a number of military forces, of which the British Army (also referred to historically as the 'Regular Army' and the 'Regular Force') was only one. The oldest of these organisations was the Militia Force (also referred to as the Constitutional Force), which (in the Kingdom of England) was originally the main military defensive force (there otherwise were originally only royal bodyguards, including the Yeomen Warders and the Yeomen of the Guard, with armies raised only temporarily for expeditions overseas), made up of civilians embodied for annual training or emergencies, and had used various schemes of compulsory service during different periods of its long existence.