Question: Captain Douglas Ricardo "Doug" Beattie MC is an Irish soldier and politician, "Born in barracks"" in 1965, his father was a warrant officer in which infantry rifle regiment of the British Army, first created in 1881 by the amalgamation of the 83rd (County of Dublin) Regiment of Foot and the 86th (Royal County Down) Regiment of Foot, but became which organization on 1 January 1921?

full_context: Document 1: Royal Ulster Rifles: The Royal Irish Rifles (became the Royal Ulster Rifles from 1 January 1921) was an infantry rifle regiment of the British Army, first created in 1881 by the amalgamation of the 83rd (County of Dublin) Regiment of Foot and the 86th (Royal County Down) Regiment of Foot. The regiment saw service in the Second Boer War, the First World War, the Second World War and the Korean War.
Document 2: King's Royal Rifle Corps: The King's Royal Rifle Corps was an infantry rifle regiment of the British Army that was originally raised in British North America as the Royal American Regiment (also known as the Royal Americans) in the Seven Years' War and for Loyalist service in the American Revolutionary War. Later, ranked as the 60th Regiment of Foot, the regiment served for more than 200 years throughout the British Empire. In 1958, the regiment joined the Oxfordshire and Buckinghamshire Light Infantry and the Rifle Brigade in the Green Jackets Brigade and in 1966 the three regiments were formally amalgamated to become the Royal Green Jackets. The KRRC became the 2nd Battalion Royal Green Jackets. On the disbandment of 1/RGJ in 1992, the RGJ's KRRC battalion was redesignated as 1/RGJ, eventually becoming 2/RIFLES in 2007.
Document 3: Baron Dunleath: Baron Dunleath, of Ballywalter in the County of Down, is a title in the Peerage of the United Kingdom. It was created in 1892 for the businessman and former Conservative Member of Parliament for Downpatrick, John Mulholland. The Mulholland family were involved in the cotton and linen industry in Ulster in the north of Ireland. The first Baron's son, the second Baron, represented Londonderry North in the House of Commons as a Conservative. His grandson, the fourth Baron, was a member of the Northern Ireland Assembly for the Alliance Party. He was succeeded by his first cousin, the fifth Baron, who had already succeeded his father as second Baronet of Ballyscullion (see below). s of 2014 the titles are held by the fifth Baron's son, the sixth Baron, who succeeded in 1997.
Document 4: Gerry Adams: Gerard "Gerry" Adams (Irish: "Gearóid Mac Ádhaimh" ; born 6 October 1948) is an Irish republican politician who is the president of the Sinn Féin political party and a Teachta Dála (TD; a member of the Irish parliament) for Louth since the 2011 general election.
Document 5: Doug Beattie: Captain Douglas Ricardo "Doug" Beattie MC is an Irish soldier and politician. ""Born in barracks"" in 1965, his father was a warrant officer in the Royal Ulster Rifles. The family settled in Portadown when he was 10 following the cessation of his father's regular service but saw Beattie Snr enlist into the Ulster Defence Regiment shortly after.
Document 6: Donnelly's Bar and Kay's Tavern attacks: On 19 December 1975, two coordinated attacks were carried out by the Ulster Volunteer Force (UVF) in pubs either side of the Irish border. The first attack, a car bombing took place outside Kay's Tavern, a pub in Dundalk in the Republic of Ireland close to the border. The second attack, a gun and bomb attack, took place at Donnelly's Bar & Filling Station in Silverbridge, County Armagh just across the border inside Northern Ireland. The attack has been linked to the Glenanne gang, a group of Loyalist militants who were either members of the UVF, the Ulster Defence Regiment (UDR), the Royal Ulster Constabulary (RUC) and the closely linked UVF paramilitary the Red Hand Commando (RHC), some of the Glenanne gang were members of the two of these organizations at the same time like gang leaders Billy Hanna who was in both the UVF and the UDR and who fought for the British Army during the Korean War and John Weir (loyalist) who was in the UVF and was a Sergeant in the RUC. At least 25 British soldiers and police officers were named as members of the gang.
Document 7: 83rd (County of Dublin) Regiment of Foot: The 83rd (County of Dublin) Regiment of Foot was a British Army line infantry regiment, which was formed in Ireland in 1793 for service in the French Revolutionary Wars. The regiment served in the West Indies, South Africa and the Peninsular War, and after the end of the wars with France spent much of the nineteenth century in colonial garrisons. Among other service, the 83rd fought in the Ceylon Great Rebellion of 1817–18, the Canadian Rebellions of 1837, and the Indian Rebellion of 1857. Under the Childers Reforms, the regiment amalgamated with the 86th (Royal County Down) Regiment of Foot to form the Royal Irish Rifles in 1881.
Document 8: Royal Irish Regiment (1992): The Royal Irish Regiment (27th (Inniskilling) 83rd and 87th and Ulster Defence Regiment) (R IRISH) is an infantry regiment of the British Army. The regiment was founded in 1992 through the amalgamation of the Royal Irish Rangers and the Ulster Defence Regiment. Their oldest predecessor; the 27th Regiment of Foot; was first raised in June 1689 to fight in the Williamite War in Ireland. Other notable regiments in their lineage include the Royal Inniskilling Fusiliers, Royal Irish Rifles and the Royal Irish Fusiliers (Princess Victoria's).
Document 9: 86th (Royal County Down) Regiment of Foot: The 86th (Royal County Down) Regiment of Foot was an infantry regiment of the British Army, raised in 1793. Under the Childers Reforms it amalgamated with the 83rd (County of Dublin) Regiment of Foot to form the Royal Irish Rifles in 1881.
Document 10: Joe Cahill: Joe Cahill (Irish: Seosamh Ó Cathail ; 19 May 1920 – 23 July 2004) was a prominent figure in the Irish Republican movement in Northern Ireland and former chief of staff of the Provisional Irish Republican Army (IRA). He joined a junior-republican movement, Na Fianna Eireann, in 1937 and the following year, joined the Irish Republican Army. In 1969, Cahill was a key figure in the founding of the Provisional Irish Republican Army. During his time in the Provisional IRA, Cahill helped import weapons and raise financial support. He served as the chief of staff in 1972, but was arrested the following year when a ship importing weapons was intercepted. After his release, he continued to serve on the IRA Army Council and lead all financial dealings for Sinn Féin. In the 1990s, the IRA and Sinn Féin began to work on seeking peace. Cahill served on the council that called a cessation on 21 July 1996. Cahill attended several of the talks that finally led to the Good Friday Agreement on 10 April 1998. Shortly after the agreement was made, Cahill resigned as treasurer of Sinn Féin. To honour his service, he was made honorary Sinn Féin Vice-President for life.
Document 11: Tom Elliott (politician): Thomas Beatty Elliott (born 11 December 1963) is a United Kingdom politician who was a Member of the Northern Ireland Assembly (MLA) for Fermanagh and South Tyrone from 2003–15, its Member of Parliament (MP) from 2015–17 and was the Leader of the Ulster Unionist Party from 2010–12.
Document 12: Dougie Wood: Dougie Wood (born 15 February 1940) is a Scottish former footballer, who played for eleven seasons with Derry City from 1961-1972 in the Irish League. He won six inter-league caps for the Irish League between 1964 and 1967, and won the Irish Cup in 1963/64, the Irish League championship and the Gold Cup in 1964/65. He was the Ulster Footballer of the Year for the 1964/65 season. He also managed the club as player-manager between July 1971 and July 1972.
Document 13: Royal Irish Rangers: The Royal Irish Rangers (27th (Inniskilling), 83rd and 87th) was a regular infantry regiment of the British Army with a relatively short existence, formed in 1968 and later merged with the Ulster Defence Regiment in 1992 to form the Royal Irish Regiment.
Document 14: Royal Regiment of Wales: The Royal Regiment of Wales (24th/41st Foot) was an infantry regiment of the British Army, part of the Prince of Wales' Division. It was formed in 1969 by the amalgamation of the South Wales Borderers and the Welch Regiment. The 1st Battalion, The Royal Regiment of Wales (24th/41st Foot) had a short existence in military terms, just over 36 years. Within two months of amalgamation, the battalion was one of the first units to be deployed to Northern Ireland.
Document 15: John Stewart (Northern Ireland politician): John Stewart (born 9 April 1983) is a Northern Irish Unionist politician, businessman, and soldier. Since 2017, he has been an Ulster Unionist Party Member of the Northern Ireland Assembly (MLA) for East Antrim.
ground_truth: Royal Ulster Rifles