The 21st Division was an infantry division of the British Army during World War I, raised in September 1914 by men volunteering for Lord Kitchener's New Armies. The division moved to France in September 1915 and served on the Western Front for the duration of the First World War.
The division's insignia was the "triple-seven".
The Division was the first of the six created for the Third New Army on 13 September 1914. The division suffered 55,581 killed, wounded and missing, being the highest number of casualties suffered by any New Army division. The Division ceased to exist on 19 May 1919.
62nd Brigade
12th (Service) Battalion, Northumberland Fusiliers
13th (Service) Battalion, Northumberland Fusiliers
8th (Service) Battalion, East Yorkshire Regiment (until November 1915)
1st Battalion, Lincolnshire Regiment (from November 1915)
10th (Service) Battalion, Alexandra, Princess of Wales's Own (Yorkshire Regiment) (disbanded February 1918)
2nd Battalion, Lincolnshire Regiment (from February 1918)
3/4th Battalion, Queen's (Royal West Surrey Regiment) (from August 1917)
63rd Brigade
In July 1916 the brigade moved to the 37th Division, swapping with the 110th Brigade.
8th (Service) Battalion, Lincolnshire Regiment
8th (Service) Battalion, Prince Albert's (Somerset Light Infantry)
12th (Service) Battalion, Prince of Wales's Own (West Yorkshire Regiment) (until November 1915)
4th Battalion, Duke of Cambridge's Own (Middlesex Regiment) (from November 1915)
10th (Service) Battalion, York and Lancaster Regiment
64th Brigade
9th (Service) Battalion, King's Own (Yorkshire Light Infantry)
10th (Service) Battalion, King's Own (Yorkshire Light Infantry) (disbanded February 1918)
14th (Service) Battalion, Durham Light Infantry (until November 1915)
15th (Service) Battalion, Durham Light Infantry
1st Battalion, East Yorkshire Regiment (from November 1915)
110th Brigade
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 (until June 1918)
9th (Service) Battalion, Leicestershire Regiment (disbanded February 1918)
1st Battalion, Duke of Edinburgh's (Wiltshire Regiment) (from June 1918)
Pioneers
14th (Service) Battalion, Northumberland Fusiliers
The division took part in the Battle of Loos, Battle of the Somme, Battle of Arras, Battle of Passchendaele and Battle of Cambrai.
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)
1 April 1916 Major-General Claud Jacob
22 May 1916 Major-General David Campbell
