at the
Battle of Waterloo, 1815
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 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. 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 a number of 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, 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 , showing the defeat of the Franco-Spanish assault in September 1782 During the later 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 a number of 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 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. 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. 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 being briefed before the
Normandy landings in 1944 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 was the mainstay of Britain's airborne nuclear capability for much of the
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. However the
Dhofar Rebellion (1962–1976) and
The Troubles (1969–1998) emerged as the primary operational concerns of the armed forces. 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. 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) has 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. ==Today==