King Charles III, sovereign of the United Kingdom, is the commander-in-chief and is styled as Head of the Armed Forces,[11][12] 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.

[13][14] 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.

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).

[45] 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.

During this period, Britain also sought to maintain the balance of power in Europe, particularly against Russian expansionism,[49] who at the expense of the waning Ottoman Empire had ambitions to "carve up the European part of Turkey".

[52] 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.

Defence Reviews, such as those in 1957 and 1966, announced significant reductions in conventional forces,[58] the pursuement of a doctrine based on nuclear deterrence,[59][60] and a permanent military withdrawal east of Suez.

[56][63][64] 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,[65] 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.

[63] While NATO obligations took increased prominence, Britain nonetheless found itself engaged in a number of low-intensity conflicts, including a spate of insurgencies against colonial occupation.

[67] 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.

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).

[71] 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.

Long-standing constitutional convention, however, has de facto vested military authority and associated royal prerogative powers in the prime minister and the secretary of state for defence, with the former (acting with the support of the Cabinet) making the key decisions on the use of the armed forces.

[80] For comparison: Great Britain spends more in absolute terms than Germany, Ukraine, France or Japan, similar to Saudi Arabia, but less than India, Russia, China or the United States.

[85] According to the British Government, since the introduction of Polaris (Trident's predecessor) in the 1960s, from April 1969 "the Royal Navy's ballistic missile boats have not missed a single day on patrol",[85] giving what the Defence Council described in 1980 as a deterrent "effectively invulnerable to pre-emptive attack".

[86] As of 2015, it has been British Government policy for the Vanguard-class strategic submarines to carry no more than 40 nuclear warheads, delivered by eight UGM-133 Trident II ballistic missiles.

[87] In contrast with the other recognised nuclear weapon states, the United Kingdom operates only a submarine-based delivery system, having decommissioned its tactical WE.177 free-fall bombs in 1998.

[98][99][100][101][102] As, until the end of the First World War, it was presumed the only navies that might prove a threat were all of countries on, or off, the Atlantic, no Imperial fortress was established in the Pacific or Indian Oceans, to which power would be extended from Bermuda and Malta following the completion of the Panama and Suez canals.

Under the North Atlantic Treaty Organisation alliance, and with the steady reduction of both the British Empire and the British Armed Forces over the decades that followed the Second World War, the significance of the three remaining Imperial fortresses (military control of Halifax having passed to the new Dominion government following the 1867 Confederation of Canada, and naval control transferred in 1905 to what was to become the Royal Canadian Navy) rapidly faded.

The British Armed Forces today maintain a number of overseas garrisons and military facilities which enable the country to conduct operations worldwide.

[106] A large Royal Navy Naval Support Facility (NSF) is located in Bahrain, established in 2016 it marks the British return East of Suez.

[118] Since 1969 Britain has had a military satellite communications system, Skynet, initially in large part to support East of Suez bases and deployments.

The Royal Navy has commissioned two Queen Elizabeth-class aircraft carriers, embarking an air-group including the advanced fifth-generation multi-role fighter, the F-35B Lightning.

Consisting of a single manoeuvre brigade (UK Commando Force) and various independent units, the Royal Marines specialise in amphibious, arctic, and mountain warfare.

[135][132][136] The four battalions of the Parachute Regiment, forming 16 Air Assault Brigade Combat Team and part of Special Forces Support Group, are the British Army's elite airborne infanteers, held at high readiness and specialising in rapid deployment by parachute and helicopter, widely regarded as the "fittest, most aggressive, resilient and disciplined regiment in the British Army.

There are six Light Cavalry regiments (three Regular + three Reserve) equipped with the Jackal 2 and Coyote TSV, tasked with providing reconnaissance and fire support.

[156] Excluding the Brigade of Gurkhas and the Royal Irish Regiment, as of 1 April 2014 there are approximately 11,200 Black and Minority Ethnic (BME) persons serving as Regulars across the three service branches; of those, 6,610 were recruited from outside the United Kingdom.

[157][158] The forces keep no formal figures concerning the number of gay and lesbian serving soldiers, saying that the sexual orientation of personnel is considered irrelevant and not monitored.

[159] Women have been part of the armed forces, on and off, for centuries, more fully integrated since the early 1990s, including flying fast jets and commanding warships or artillery batteries.