Military unit
100th (Yeomanry) Regiment Royal Artillery is a reserve unit of the British Army that provides tactical air control parties, naval gunnery liaison officers, specialist staff officers and gunnery instructors. 
It was formerly part of the Territorial Army and had three gun batteries all equipped with the L118 Light Gun.
History.
First incarnation.
The regiment was formed as 100th (Eastern) Medium Regiment Royal Artillery at Grove Park in London in 1967. Its sub-units were RHQ, HQ (Home Counties) Battery at Grove Park, Lewisham, (formed from Regimental HQ of 265th (8th London) Light Anti-Aircraft Regiment, Royal Artillery, together with HQ Royal Artillery of 44th (Home Counties) Division/District), 200 (Sussex Yeomanry) Medium Battery at Brighton, 201 (Hertfordshire and Bedfordshire Yeomanry) Medium Battery at Luton, 202 (Suffolk and Norfolk Yeomanry) Medium Battery at Bury St Edmunds and REME LAD which expanded into a workshop during the FH70 period. In 1970 it became 100th Regiment Royal Artillery and in 1976 it became 100 (Yeomanry) Field Regiment Royal Artillery.
In 1993 200 Battery left the regiment and 307 (South Nottinghamshire Hussars) Battery at Bulwell joined the unit. It was renamed 100 (Yeomanry) Regiment Royal Artillery in 1993 and in 1999, HQ and 202 Batteries left the regiment; 202 was replaced by 266 (Gloucestershire Volunteer Artillery) Battery at Bristol.
The regiment's original role was British Army of the Rhine (BAOR) emergency reinforcement, emphasised by its transfer into 49 Infantry Brigade under part of 2 Division. Under 'Options for Change', the regiment became a general support unit fitted out with the FH-70 155 mm towed howitzer and assigned to 3 Division.
Under Army 2020, this unit was placed in suspended animation and 266 (Gloucestershire Volunteer Artillery) Battery Royal Artillery joined 104th Regiment Royal Artillery.
Batteries.
The batteries were as follows:
Second incarnation.
Central Volunteer Headquarters, Royal Artillery.
Prior to the review of the Territorial Army in 1967, all territorial troops who joined the Royal Artillery were organised through the Royal Artillery Depot based at Royal Artillery Barracks, Woolwich Garrison. However, as part of the reorganisation of the TA in 1967, all TA specialist units and formations were grouped under a single unit.
The new unit was formed as part of TAVR IIB, meaning it was able to deploy independent assets, but would be unable to deploy as a full unit (TAVR IIA would have this role).
After the 1966 Defence White Paper, the Central Volunteer Headquarters, Royal Artillery (CVHQ, RA) was formed at the before-mentioned barracks and placed under Headquarters, London District as a nationally recruited specialist TA unit.
After formation, the headquarters was organised as follows:
Following the Army 2020 reform, and later the Army 2020 Refine, the Central Volunteer Headquarters, Royal Artillery was retitled as the National Reserve Headquarters, Royal Artillery, and reorganised into the following structure:
On 4 September 2023, the National Reserve Headquarters, Royal Artillery (NRHQ RA) had been redesignated the 100 (Yeomanry) Regiment, Royal Artillery, thereby reviving the old regiment.
Current structure and role.
The current structure is as follows:
100th (Yeomanry) Regiment, Royal Artillery.
221 Battery provides specialist gunnery staff support across the Field Army, but principally to Regular and Reserve Royal Artillery units and the Royal School of Artillery on operations and exercises.
255 Battery provides 10x Tactical Air Control Parties (TACPs), consisting of Joint Terminal Attack Controllers (JTACs) and TACP Signallers to support ground forces in the control of Close Air Support (CAS) aircraft; personnel deploy either as formed TACPs or as individual augmentees.
The All Arms Staff Pool (AASP) provides individual replacements to support staff officer functionality in Field Army formation Headquarters. The AASP also includes The Kings’ Troop Royal Horse Artillery support troop, Ground Liaison Officers and Naval Gunfire Liaison Officers (NGLO’s). NGLO’s deploy on Royal Navy and partner-nation warships to work with 29 Commando Regiment Royal Artillery and enable naval gunnery. Ground Liaison Officers support the Royal Air Force.
Only half of the regiment's 368 officers and soldiers are in the Royal Artillery, the rest representing almost every other cap badge in the British Army.
References.
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