The longest continuous deployment in British military history spanned almost four decades and cost the lives of hundreds of soldiers – many as a result of paramilitary attacks.
Under Operation Banner, troops were deployed to assist the police in Northern Ireland (NI), in what was initially intended as a "limited operation" to restore law and order.
The first troops arrived on the streets of Londonderry and Belfast in the summer of 1969, but the British Government's intention to pull out the troops within days turned out to be short-lived, as it became clear that the violence that had escalated in the streets following the soldiers' arrival was not going to subside.
Operation Banner ended up lasting from August 1969 to July 2007.
Troops were initially sent in after the August 1969 riots, at the request of the unionist government at Stormont, Belfast.
At first, the nationalist community saw the troops as a necessary safeguard from aggression and violence from loyalist troublemakers.
The conflict in Northern Ireland, known as 'the Troubles', lasted from 1969 to 1998, and, at the heart of it, was constitutional status.
Whilst the goal of the unionist majority was to remain part of the United Kingdom, the nationalist and republican minority wanted to become part of the Republic of Ireland.
Several attempts to find a political solution failed, until the Good Friday Agreement in 1998, which won approval from all sides and led to the restoration of self-government for Northern Ireland, bringing an end to the Troubles.
More than 300,000 British troops served in Northern Ireland during Op Banner, with more than 20,000 deployed at its peak.
A total of 1,441 soldiers died during Op Banner, 722 as a result of paramilitary attacks.
Here is a look at some of the key moments during the course of the operation:
12-14 August 1969 - Battle of the Bogside
Tensions boiled over during the Apprentice Boys march in Derry.
The annual march commemorates the Siege of Derry in 1689.
Around 15,000 Protestants marched along the walls, past the perimeter of the predominantly-nationalist Bogside area.
Rioting ensued and went on for three days in the Bogside. Petrol bombs were thrown as violence broke out.
The Stormont government then requested the assistance of the British Army.
1st Battalion the Prince of Wales’s Own Regiment of Yorkshire was sent to separate loyalists and nationalists, and became the first Army unit to deploy onto the streets of Northern Ireland during the campaign.
3-5 July 1970 - The 'Falls Curfew'
A search began for weapons at homes in the area of the nationalist Falls Road, Belfast. Soldiers seized firearms, leading to a backlash of violence, descending into a riot. The Army and the Irish Republican Army (IRA) engaged in a gun battle.
A military curfew was imposed on the area on Friday 3 at around 10pm, and was lifted on Sunday 5.
It was regarded as a turning point in the nationalist perception of troop presence.
Before, the Army tended to be seen as a neutral agent, acting in somewhat of a 'protector' mould.
After the curfew, local discourse pointed to a definitive change in how nationalists and republicans viewed the intentions and actions of troops.
6 February 1971 - First military fatality in the conflict
Gunner Robert Curtis was shot dead by the Provisional IRA during a disturbance in the New Lodge area of Belfast.
Prime Minister Edward Heath refused NI Prime Minister James Chichester-Clark's request for a greater number of troops. The latter resigned soon after.
1971 - Internment and Operation Demetrius
The introduction of a controversial state policy - internment without trial.
Under Operation Demetrius, people suspected of IRA association were arrested and imprisoned without trial.
The use of internment and deep interrogation techniques had a major impact on popular opinion across Ireland, in Europe and the US.
30 January 1972 - 'Bloody Sunday'
Members of the 1st Battalion of the Parachute Regiment (1 PARA) opened fire at a civil rights march in the predominantly-nationalist Bogside, Londonderry. Thirteen people were killed, with a similar number wounded.
The IRA retaliated, bombing the regiment's Aldershot HQ, killing seven people.
Sixteen other veterans and two ex-members of the Official IRA were also all investigated, with it being ruled they would not face prosecution.
1 February 1972 - Widgery Tribunal announced
A tribunal was set up to investigate the events of Bloody Sunday, led by the Lord Chief Justice, Lord Widgery.
After hearing evidence from paratroopers and marchers, his report found the main responsibility for the deaths lay with the organisers of the march and that confrontation was almost an inevitability.
He said there would have been no deaths on Bloody Sunday "if those who organised the illegal march had not thereby created a highly dangerous situation in which a clash between demonstrators and the security forces was almost inevitable".
He went on to say, "if the Army had persisted in its 'low key' attitude and had not launched a large scale operation to arrest hooligans, the day might have passed off without serious incident".
His findings were largely rejected by nationalists and republicans, and called for a second inquiry.
Grievance over the conclusions found in Lord Widgery's report would remain until the findings of the Saville Inquiry were published in 2010.
1972 - Operation Motorman launched
It was in order to try to bring an end to "no-go" areas within republican strongholds in urban areas.
These locations posed a challenge for security forces as the zones harboured IRA operatives.
Bulldozers and other heavy vehicles were used to break through barricades.
The IRA carried out bombings in response.
The number of British troops in Northern Ireland at this time totalled 21,000.
15-28 May 1974 - Ulster Workers Council strike
The council - opposed to the Sunningdale Agreement, power-sharing with nationalists - called upon loyalists working at power stations to go on strike.
With fuel in short supply, troops distributed petrol.
The strike brought down the Northern Ireland Assembly and Executive, returning governance to Westminster.
5 January 1976 - Kingsmill Massacre
The IRA killed 10 Protestant workers at Kingsmill, County Armagh. Extra troops were deployed in response.
17 May 1976 - Bus shooting
A private shot dead a Catholic man as he sat on a bus passing Fort George Army base, County Londonderry.
The man, James Gallagher, had previously served time for IRA membership and planting a bomb.
27 August 1979 - Queen's cousin dies and IRA ambush in Warrenpoint
The Queen's cousin, Lord Louis Mountbatten, was killed in an IRA bomb attack in County Sligo, Republic of Ireland.
On holiday in Mullaghmore, an explosive device ripped through his leisure boat.
On the same day, an IRA landmine and shooting ambush at Narrow Water, Warrenpoint, County Down, killed 18 soldiers.
An 800lb bomb detonated in a trailer at the side of the road near Carlingford Lough, the boundary with the Republic.
It was the highest death toll suffered by the British Army in a single incident since it had arrived in Northern Ireland.
An English holidaymaker, Michael Hudson, died in the ensuing crossfire between the Army and the IRA.
6 December 1982 - Droppin' Well bombing
Eleven soldiers were among the 17 dead at the Droppin' Well pub in Ballykelly, killed by a republican group, the Irish National Liberation Army.
The bar was well-known for being popular with members of the Army from the nearby Shackleton Barracks.
Watch: in 2012, Forces News reporters were in Northern Ireland as families gathered to remember the victims of the Droppin' Well bombing
15 November 1985 - Anglo-Irish Agreement signed
The UK agreed that, in most cases, all Army patrols in Northern Ireland would be given a civilian Royal Ulster Constabulary (RUC) escort.
8 May 1987 - SAS Loughgall ambush
Codenamed Operation Judy, a team from the British Army's Special Air Service (SAS) ambushed eight IRA men who were carrying out an attack on the village of Loughgall's RUC police station.
The SAS killed them as they attempted to blow up the premises.
The killing of the unit became the IRA's biggest loss of life in a single incident.
6 March 1988 - Operation Flavius
In Operation Flavius, the SAS killed three unarmed IRA members in Gibraltar.
Loyalist Michael Stone killed three people when he attacked a funeral service in west Belfast for the republicans.
Two soldiers, driving into a funeral for one of Stone's victims, were dragged from their car, beaten and shot dead.
1989 - Stevens Inquiries ordered
Senior Metropolitan police commander Sir John Stevens headed up a probe into collusion between members of the security forces in Northern Ireland and loyalists following concerns about the shooting dead of Belfast solicitor Pat Finucane and other sectarian murders.
7 October 1996 - Thiepval barracks bombed
A soldier was killed when two IRA bombs exploded inside the Army's NI HQ in Lisburn, Thiepval Barracks.
12 February 1997 - Final military fatality during Op Banner
Lance Bombardier Stephen Restorick was the last soldier to lose his life during Operation Banner, killed by an IRA sniper whilst on duty at a checkpoint in Bessbrook, County Armagh.
10 April 1998 - Good Friday Agreement signed
The agreement committed signatories to decommissioning of weapons and demilitarisation, and "exclusively democratic and peaceful means of resolving differences on political issues".
It effectively brought an end to the Troubles and set out the terms for a power-sharing assembly to sit at Stormont.
1998 - Saville Inquiry announced by Prime Minister Tony Blair
It was established in response to calls from families of the deceased and injured on Bloody Sunday for a second inquiry.
April 2003 - Stevens Report
Sir John Stevens submitted his report finding that members of the Army and police colluded with the Ulster Defence Association. The Army's Force Research Unit was linked to agent handling.
July 2005 - The IRA calls an end to its armed campaign
The following month, NI Secretary Peter Hain announced a two-year demilitarisation programme.
A decision is made for the number of British troops stationed in Northern Ireland to stay at 5,000.
Cloghogue, a watchtower near the border with the Republic of Ireland, was demolished.
31 July 2007 - Operation Banner comes to an end
The Army's stronghold at Bessbrook, County Armagh, was closed, with Operation Banner brought to an end on 31 July.
Following its conclusion, Operation Helvetic has ensured an Army presence remains in Northern Ireland.
Its activities include bomb disposal teams.
7 March 2009 - Sappers shot outside Massereene Army barracks
Two sappers in 38 Engineer Regiment, Mark Quinsey and Patrick Azimkar, were murdered by dissident republican gunmen from the Real IRA outside Massereene Army barracks in County Antrim.
The soldiers, hours from deploying to Afghanistan, were targeted when they stepped outside the gates of the base to collect a pizza delivery.
15 June 2010 - Saville Report publication
The Saville Report was published, blaming members of 1 PARA for "unjustifiable firing" which caused the deaths of 13 people, "none of whom was posing a threat of causing death or serious injury" on Bloody Sunday.
The report states, in contrast to previously held beliefs, none of the soldiers fired in response to attacks by petrol bombers or stone-throwers, and that the civilians were not posing any threat.
Lord Saville also said: "Our overall conclusion is that there was a serious and widespread loss of fire discipline among the soldiers of Support Company.
"What happened on Bloody Sunday strengthened the Provisional IRA, increased nationalist resentment and hostility towards the Army and exacerbated the violent conflict of the years that followed.
"Bloody Sunday was a tragedy for the bereaved and the wounded, and a catastrophe for the people of Northern Ireland."
Prime Minister David Cameron addressed the House of Commons, and made an apology on behalf of the British government.
Watch: in 2010, the Independent Monitoring Commission warned of a potential increase in attacks in Northern Ireland
Members of the Army have been under investigation for high-profile cases of alleged wrongful killing.
On the other side stand the victims of state killings seeking justice for the deaths of loved ones.
Up until January 2020, Northern Ireland was without a government, with the Stormont Assembly and Executive having not sat for three years.
The powersharing deadlock began in January 2017, when the two main parties - the DUP and Sinn Fein - split in a row.