4 March 1916, transferred into 21st MG Battalion 24 February 1918) 64th Trench Mortar Battery (joined by 16 June 1916) 110th Brigade (the Leicester Tigers) In July 1916 the brigade joined from the 37th Division, swapping with the 63rd Brigade. 6th (Service) Battalion, Leicestershire Regiment 7th (Service) Battalion, Leicestershire Regiment 8th (Service) Battalion, Leicestershire Regiment (leftJune 1918) 9th (Service) Battalion, Leicestershire Regiment (disbanded February 1918) 1st Battalion, Duke of Edinburgh's (Wiltshire Regiment) (from June 1918) 110th Machine Gun Company (transferred into 21st MG Battalion 24 February 1918) 110th Trench Mortar Battery Divisional Troops 14th (Service) Battalion, the Northumberland Fusiliers became Divisional Pioneer Battalion in February 1915 13th (Service) Battalion, King’s Royal Rifle Corps (left April 1915) 13th (Service) Battalion, Rifle Brigade (left April 1915) 237th Machine Gun Company (joined 17 July 1917, transferred into 21st MG Battalion 24 February 1918) 21st Battalion Machine Gun Corps (formed 24 February 1918) Divisional Mounted Troops A Sqn, South Irish Horse (joined January 1915, left May 1916) 21st Divisional Cyclist Company, Army Cyclist Corps (formed February 1915, left 10 May 1916) 21st Divisional Train Army Service Corps 182nd, 183rd, 184th and 185th Companies 33rd Mobile Veterinary Section Army Veterinary Corps 222nd Divisional Employment Company (joined 30 June 1917) Royal Artillery XCIV Brigade, Royal Field Artillery (R.F.A.) XCV Brigade, R.F.A. XCVI Brigade, R.F.A. (broken up 13 January 1917) XCVII (Howitzer) Brigade, R.F.A (broken up 28–31 August 1916) 21st Divisional Ammunition Column R.F.A. 21st Heavy Battery, Royal Garrison Artillery (R.G.A.) (transferred to XXIII Heavy Artillery Brigade on 21 August 1915) V.21 Heavy Trench Mortar Battery R.F.A. (joined 1 June 1916, left February 1918) W.21 Medium Mortar Battery R.F.A. (joined May, left August 1916) X.21, Y.21 and Z.21 Medium Mortar Batteries R.F.A. 4 x 6-inch mortars each (joined 1–13 March 1916; in February 1918, Z broken up and batteries reorganised to have 6 x 6-inch mortars each) Royal Engineers 85th Field Company (left January 1915) 86th Field Company (left February 1915) 97th Field Company 98th Field Company 126th Field Company (joined March 1915) 21st Divisional Signals Company Royal Army Medical Corps 63rd Field Ambulance 64th Field Ambulance 65th Field Ambulance 38th Sanitary Section (left 1 April 1917) Commanders During its existence, 21st Division had the following commanders: 16 September 1914 Lt Gen Edward Hutton 11 April 1915 Major-General George Forestier-Walker 18 November 1915 Major-General Claud Jacob (wounded, 4 March 1916) 4 March 1916 Brig.-General G.M. Gloster (temporary)