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British Armed Forces

Combined military forces of the United Kingdom

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Since the formation of the united Kingdom of Great Britain in 1707 (later succeeded by the United Kingdom of Great Britain and Ireland in 1801, and finally by the United Kingdom of Great Britain and Northern Ireland in 1927), 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 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, the Regular, Volunteer 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 of 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.

History

Organisation

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 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 for 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 several 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.

The Militia was originally an all infantry force, organised at the city or county level, and members were not required to serve outside of their recruitment area, although the area within which militia units in Britain could be posted was increased to anywhere in the Britain during the 18th century, and Militia coastal artillery, field artillery, and engineers units were introduced from the 1850s. The Yeomanry was a mounted force that could be mobilised in times of war or emergency. Volunteer Force units were also frequently raised during wartime, which did not rely on compulsory service and hence attracted recruits keen to avoid the Militia. These were seen as a useful way to add to military strength economically during wartime, but otherwise as a drain on the Militia and so were not normally maintained in peacetime, although in Bermuda prominent propertied men were still appointed Captains of Forts, taking charge of maintaining and commanding fortified coastal artillery batteries and manned by volunteers (reinforced in wartime by embodied militiamen), defending the colony's coast from the 17th century to the 19th century (when all of the batteries were taken over by the regular Royal Artillery). The militia system was extended to several English (subsequently British) colonies, beginning with Virginia and Bermuda. In some colonies, Troops of Horse or other mounted units similar to the Yeomanry were also created. The militia and volunteer units of a colony were generally considered to be separate forces from the Home Militia Force and Volunteer Force in the United Kingdom, and from the militia forces and volunteer forces of other colonies. Where a colony had more than one militia or volunteer unit, they would be grouped as a militia or volunteer force for that colony, such as the Jamaica Volunteer Defence Force, which comprised the St. Andrew Rifle Corps, or Kingston Infantry Volunteers, the Jamaica Corps of Scouts, and the Jamaica Reserve Regiment, but not the Jamaica Militia Artillery. In smaller colonies with a single militia or volunteer unit, that single unit would still be considered to be listed within a force, or in some case might be named a force rather than a regiment or corps, such as is the case for the Falkland Islands Defence Force and the Royal Montserrat Defence Force. The militia, yeomanry, and volunteer forces collectively were known as the reserve forces, auxiliary forces, or local forces. Officers of these forces could not sit on courts-martial of regular forces personnel. The Mutiny Act did not apply to members of the Reserve Forces.

The other regular military force that existed alongside the British Army was the Board of Ordnance, which included the Ordnance Military Corps (made up of the Royal Artillery, Royal Engineers, and the Royal Sappers and Miners), as well as the originally-civilian Commissariat Stores and transport departments, as well as barracks departments, ordnance factories and various other functions supporting the various naval and military forces. The English Army, subsequently the British Army once Scottish regiments were moved onto its establishment following the Union of the Kingdoms of Scotland and England, was originally a separate force from these, but absorbed the Ordnance Military Corps and various previously civilian departments after the Board of Ordnance was abolished in 1855. The Reserve Forces (which referred to the Home Yeomanry, Militia and Volunteer Forces before the 1859 creation of the British Army Regular Reserve by Secretary of State for War Sidney Herbert, and re-organised under the Reserve Force Act 1867) were increasingly integrated with the British Army through a succession of reforms over the last two decades of the 19th century (in 1871, command of the Auxiliary Forces in the British Isles was taken from the Lords-Lieutenant of counties and transferred to the War Office, though colonial governors retained control of their militia and volunteer forces, and by the end of the century, at the latest, any unit wholly or partly funded from Army funds was considered part of the British Army) and the early years of the 20th century, whereby the Reserve Forces units mostly lost their own identities and became numbered Territorial Force sub-units of regular British Army corps or regiments (the Home Militia had followed this path, with the Militia Infantry units becoming numbered battalions of British Army regiments, and the Militia Artillery integrating within Royal Artillery territorial divisions in 1882 and 1889, and becoming parts of the Royal Field Artillery or Royal Garrison Artillery in 1902 (though retaining their traditional corps names), but was not merged into the Territorial Force when it was created in 1908 (by the merger of the Yeomanry and Volunteer Force). The Militia was instead renamed the Special Reserve, and was permanently suspended after the First World War (although a handful of Militia units survived in the United Kingdom, its colonies, and the Crown Dependencies). Unlike the Home, Imperial Fortress, and Crown Dependency Militia and Volunteer units and forces that continued to exist after the First World War, although parts of the British military, most were not considered parts of the British Army unless they received Army funds, as was the case for the Bermuda Militia Artillery and the Bermuda Volunteer Rifle Corps, which was generally only the case for those in the Channel Islands or the Imperial Fortress colonies (Nova Scotia, before Canadian Confederation, Bermuda, Gibraltar, and Malta). Today, the British Army is the only Home British military force (unless the Army Cadet Force and the Combined Cadet Force are considered), including both the regular army and the forces it absorbed, though British military units organised on Territorial lines remain in British Overseas Territories that are still not considered formally part of the British Army, with only the Royal Gibraltar Regiment and the Royal Bermuda Regiment (an amalgam of the old Bermuda Militia Artillery and Bermuda Volunteer Rifle Corps) appearing on the British Army order of precedence and in the Army List.

Confusingly, and similarly to the dual meaning of the word Corps in the British Army. As an example, the 1st Battalion of the King's Royal Rifle Corps was in 1914 part of the 6th Brigade that was part of the 2nd Infantry Division, which was itself part of 1st Army Corps), the British Army sometimes also used the term expeditionary force or field force to describe a body made up of British Army units, most notably the British Expeditionary Force, or of a mixture of British Army, Indian Army, or Imperial auxiliary units, such as the Malakand Field Force (this is similarly to the naval use of the term task force). In this usage, force is used to describe a self-reliant body able to act without external support, at least within the parameters of the task or objective for which it is employed.

British Empire

During the latter half of the 17th century, and in particular, throughout the 18th century, British foreign policy sought to contain the expansion of rival European powers through military, diplomatic, and commercial means, especially of its chief competitors Spain, the Netherlands, and France. This saw Britain engage in several intense conflicts over colonial possessions and world trade, including a long string of Anglo-Spanish and Anglo-Dutch wars, as well as a series of "world wars" with France, such as; the Seven Years' War (1756–1763), the French Revolutionary Wars (1792–1802) and the Napoleonic Wars (1803–1815). During the Napoleonic wars, the Royal Navy's victory at Trafalgar (1805) under the command of Horatio Nelson (aboard HMS Victory) marked the culmination of British maritime supremacy, and left the Navy in a position of uncontested hegemony at sea. By 1815 and the conclusion of the Napoleonic Wars, Britain had risen to become the world's dominant great power and the British Empire subsequently presided over a period of relative peace, known as Pax Britannica.

With Britain's old rivals no-longer a threat, the 19th century saw the emergence of a new rival, the Russian Empire, and a strategic competition in what became known as The Great Game for supremacy in Central Asia. Britain feared that Russian expansionism in the region would eventually threaten the Empire in India. In response, Britain undertook several pre-emptive actions against perceived Russian ambitions, including the First Anglo-Afghan War (1839–1842), the Second Anglo-Afghan War (1878–1880) and the British expedition to Tibet (1903–1904). During this period, Britain also sought to maintain the balance of power in Europe, particularly against Russian expansionism, who at the expense of the waning Ottoman Empire had ambitions to "carve up the European part of Turkey". This ultimately led to British involvement in the Crimean War (1854–1856) against the Russian Empire.

First World War

The beginning of the 20th century served to reduce tensions between Britain and the Russian Empire, partly due to the emergence of a unified German Empire. The era brought about an Anglo-German naval arms race, which encouraged significant advancements in maritime technology, including Dreadnoughts, torpedoes, submarines, and, in 1906, Britain determined that its only likely naval enemy was Germany. The accumulated tensions in European relations finally broke out into the hostilities of the First World War (1914–1918), in what is recognised today, as the most devastating war in British military history, with nearly 800,000 men killed and over 2 million wounded. Allied victory resulted in the defeat of the Central Powers, the end of the German Empire, the Treaty of Versailles and the establishment of the League of Nations.

Second World War

Germany was defeated in the First World War, but by 1933 fascism had given rise to Nazi Germany, which under the leadership of Adolf Hitler re-militarised in defiance of the Treaty of Versailles. Once again tensions accumulated in European relations, and following Germany's invasion of Poland in September 1939, the Second World War began (1939–1945). The conflict was the most widespread in British history, with British Empire and Commonwealth troops engaged in military campaigns in Europe, North Africa, the Middle East, and the Far East. Approximately 390,000 British Empire and Commonwealth troops died. Allied victory resulted in the defeat of the Axis powers and the establishment of the United Nations, replacing the League of nations.

Cold War

Post–Second World War economic and political decline, as well as changing attitudes in British society and government, were reflected by the armed forces' contracting global role, and later epitomised by its political defeat during the Suez Crisis (1956). Reflecting Britain's new role in the world and the escalation of the Cold War (1947–1991), the country became a founding member of the NATO military alliance in 1949. Defence Reviews, such as those in 1957 and 1966, announced significant reductions in conventional forces, the pursuement of a doctrine based on nuclear deterrence, and a permanent military withdrawal east of Suez. By the mid-1970s, the armed forces had reconfigured to focus on the responsibilities allocated to them by NATO. The British Army of the Rhine and RAF Germany consequently represented the largest and most important overseas commitments that the armed forces had during this period, while the Royal Navy developed an anti-submarine warfare specialisation, with a particular focus on countering Soviet submarines in the Eastern Atlantic and North Sea.

While NATO obligations took increased prominence, Britain nonetheless found itself engaged in several low-intensity conflicts, including a spate of insurgencies against colonial occupation. However, the Dhofar Rebellion (1962–1976) and The Troubles (1969–1998) emerged as the primary operational concerns of the armed forces. Perhaps the most important conflict during the Cold War, at least in the context of British defence policy, was the Falklands War (1982).

Since the end of the Cold War, an increasingly international role for the armed forces has been pursued, with re-structuring to deliver a greater focus on expeditionary warfare and power projection. This entailed the armed forces often constituting a major component in peacekeeping and humanitarian missions under the auspices of the United Nations, NATO, and other multinational operations, including: peacekeeping responsibilities in the Balkans and Cyprus, the 2000 intervention in Sierra Leone and participation in the UN-mandated no-fly zone over Libya (2011). Post-9/11, the armed forces became heavily committed to the war on terror (2001–present), with lengthy campaigns in Afghanistan (2001–2021) and Iraq (2003–2009), and more recently as part of the Military intervention against ISIL (2014–present). Britain's military intervention against Islamic State was expanded following a parliamentary vote to launch a bombing campaign over Syria; an extension of the bombing campaign requested by the Iraqi government against the same group. In addition to the aerial campaign, the British Army has trained and supplied allies on the ground, and the Special Air Service, the Special Boat Service, and the Special Reconnaissance Regiment (British special forces) have carried out various missions on the ground in both Syria and Iraq.

The armed forces have also been called upon to assist with national emergencies through the provisions of the military aid to the civil authorities (MACA) mechanism. This has seen the armed forces assist government departments and civil authorities responding to flooding, food shortages, wildfires, terrorist attacks and the COVID-19 pandemic; The armed forces' support to the latter falls under Operation Rescript, described as the UK's "biggest ever homeland military operation in peacetime" by the Ministry of Defence. Figures released by the Ministry of Defence on 31 March 2016 show that 7,185 British Armed Forces personnel have lost their lives in medal earning theatres since the end of the Second World War.

In 2025, under Prime Minister Keir Starmer, the UK published a new Strategic Defence Review (SDR) calling for a shift to "warfighting readiness". Major investments were announced, including the expansion of the SSN-AUKUS attack submarine program to up to 12 boats, acquisition of long-range weapons and advanced air-defence systems, and a possible entry into NATO's nuclear-sharing scheme via the F-35A platform.

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