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.

[2] 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.

[2] 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.

[16][17] Only half of the regiment's 368 officers and soldiers[1] are in the Royal Artillery, the rest representing almost every other cap badge in the British Army.