Question: Sir Ronald Hugh Grierson served in an infantry battalion of a regiment that was created as part of what?

Context paragraphs:
7th Arkansas Infantry Battalion: The 7th Arkansas Infantry Battalion (1861–1862) was a Confederate Army infantry battalion during the American Civil War.  The battalion, which was often referred to as Desha's Battalion, was eventually consolidated with the 9th Arkansas Infantry Battalion and the 8th Arkansas Infantry Regiment.

22nd Battalion (Australia): The 22nd Battalion was an infantry battalion of the Australian Army.  It was raised in 1915 as part of the Australian Imperial Force for service during World War I and formed part of the 6th Brigade, attached to the 2nd Division.  It fought during the Gallipoli campaign and on the Western Front before being disbanded in 1919.  In 1921, it was re-raised as a part-time unit and was merged with the 29th Battalion in 1930 to form the "29th/22nd Infantry Battalion".  Split in August 1939 and known as the "22nd Battalion (South Gippsland Regiment)", the battalion saw action against the Japanese during World War II in the Huon Peninsula and New Britain campaigns.  The battalion was disbanded in June 1946.  It was re-established as part of the Royal Victoria Regiment in the mid-1960s as a remote area battalion within the Citizens Military Force, and later became a part of the 8th/7th Battalion, Royal Victoria Regiment.

Black Watch: The Black Watch, 3rd Battalion, Royal Regiment of Scotland (3 SCOTS) is an infantry battalion of the Royal Regiment of Scotland.  The regiment was created as part of the Childers Reforms in 1881, when the 42nd (Royal Highland) Regiment of Foot (The Black Watch) was amalgamated with the 73rd (Perthshire) Regiment of Foot.  It was known as The Black Watch (Royal Highlanders) from 1881 to 1931 and The Black Watch (Royal Highland Regiment) from 1931 to 2006.  Part of the Scottish Division, it was the senior regiment of Highlanders.

Ronald Grierson: Sir Ronald Hugh Grierson (6 August 1921 – 23 October 2014) was a German-born British banker, businessman, government advisor, and British Army officer.  After service in the Black Watch, attached to the Special Air Service and mentioned in dispatches, during World War II, he became a lieutenant-colonel in the post-war SAS.  He was Managing Director of S.G. Warburg, an investment bank, from 1948 to 1985, and Vice-Chairman of General Electric Company plc, an industrial conglomerate, from 1968 to 1996.  From 1972 to 1974, he was Director-General for Industry at the European Commission.

Benjamin Henry Grierson House: The Benjamin Henry Grierson House is a historic house located at 852 East State Street in Jacksonville, Illinois.  Built circa 1850, the house was the home of U.S. Army general Benjamin Grierson from 1850 until his death.  Grierson was a Jacksonville mercantile businessman until 1861, when he joined the Union Army after the outbreak of the Civil War.  During the war, Grierson led the eponymous Grierson's Raid, a mission which cut Confederate supply lines and diverted Confederate forces during the Vicksburg Campaign.  After the war, Grierson served as colonel of the 10th Cavalry Regiment, one of the original Buffalo Soldier regiments of African-American cavalry.  Grierson was appointed brigadier general in 1890 and retired from the Army in the same year; his house in Jacksonville served as his permanent address for his entire time in the Army.

Viru Infantry Battalion: The Viru Infantry Battalion (Estonian: "Viru jalaväepataljon" ) is a battalion of the Estonian Land Forces.  It is a part of the 1st Infantry Brigade and its primary task is to train conscription-based infantry and anti-tank units.  The battalion has been previously known as the 4th Infantry Regiment and as the 4th Single Infantry Battalion.  The battalion is currently based at Jõhvi and is commanded by Lieutenant Colonel Arno Kruusmann.

8th/7th Battalion, Royal Victoria Regiment: The 8th/7th Battalion, Royal Victoria Regiment (8/7 RVR) is an infantry battalion of the Australian Army.  It is one of two battalions that make up the Royal Victoria Regiment (RVR), with its sister unit being 5th/6th Battalion, Royal Victoria Regiment.  It can trace its history back to 1854 and the battalion has existed since maintaining an unbroken record of service, albeit in varying forms and under various names.  The present day unit traces its lineage from a number of previous units, including 8th Battalion (City of Ballarat Regiment), 59th Battalion (The Hume Regiment), 7th Battalion (The North and West Murray Regiment), and the 38th Battalion (The Northern Victoria Regiment).  Today the battalion is part of the 4th Brigade and is responsible for most of the rural areas of Victoria and protecting vital assets in the north of Australia.  The battalion maintains an affiliation with the 5th/7th Battalion, Royal Australian Regiment, with whom many members of 8/7 RVR have undertaken periods of full-time service in recent times.

2nd Arkansas Infantry Battalion: The 2nd Arkansas Infantry Battalion (1861–1862) was a Confederate Army infantry battalion during the American Civil War.  The 2nd Arkansas Infantry Battalion was one of only three Arkansas units which served in Virginia during the Civil War.  The 1st Arkansas Infantry Regiment arrived in Virginia in June 1861, and was present, though not engaged, at the battle of Manassas (Bull Run) in July.  The 3rd Arkansas Infantry Regiment arrived in Virginia in July 1861, and was sent to the mountains of western Virginia.

138th Infantry Regiment (United States): The 138th Infantry Regiment is an infantry battalion in the Missouri National Guard.  Of the original regiment, only the 1st Battalion remains an active National Guard unit.  As of 2008, the 1st Battalion, 138th Infantry Regiment is a light infantry battalion currently assigned to the 110th Maneuver Enhancement Brigade headquartered in Kansas City, Missouri.

28th Battalion (Australia): The 28th Battalion was an infantry battalion of the Australian Army.  It was raised in early 1915 as part of the First Australian Imperial Force for service during the First World War and formed part of the 7th Brigade, attached to the 2nd Division.  It fought during the final stages of the Gallipoli campaign in late 1915 and then on the Western Front between 1916 and 1918.  At the end of the war, the 28th was disbanded in 1919 but was re-raised in 1921, as a part-time unit based in Western Australia.  During the Second World War, the 28th undertook defensive duties in Australia for the majority of the conflict, before seeing action against the Japanese in the New Britain campaign in 1944–45.  The battalion was disbanded in March 1946 but was re-formed in 1948 as an amalgamated unit with the 16th Battalion, before being unlinked in 1952 and re-raised as a full battalion following the reintroduction of national service.  It remained on the Australian Army's order of battle until 1960 when it was subsumed into the Royal Western Australia Regiment, but was later re-raised in 1966 as a remote area infantry battalion.  In 1977, the 28th was reduced to an independent rifle company, and in 1987 was amalgamated into the 11th/28th Battalion, Royal Western Australia Regiment.

Supporting paragraphs: Ronald Grierson Black Watch
Answer: Childers Reforms