Established in September 1914, as part of K2. Early days were somewhat chaotic, the new volunteers having very few trained officers and NCOs to command them, no organised billets or equipment. The Division first assembled in the Aldershot area with brigades at Blackdown, Deepcut and Cowshott. Artillery was particularly hard to come by; 12 old guns arrived from India in February 1915! When in the same month the Division moved to Witlet, Godalming and Guildford, the artillery had to go by train as there was insufficient harness for teh horses. Another move was made, to Salisbury Plain, in April 1915. The Division was inspected by HM King George V at Knighton Down on 24th June 1915, by which time all equipment had arrived and the Division was judged ready for war

26th July 1915 : completed concentration in the Saint-Omer area, all units having crossed to France during the preceding few days. Early trench familirisation and training took place in the Fleurbaix area. The Division then remained in the Western Front theatre, taking part in the following actions:

Attack towards Fromelles, a subsidiary to the Battle of Loos, 25 September 1915

The Battle of Mount Sorrel, including successful recapture of that height alongside the Canadians on 13th June 1916.

The Battle of Delville Wood (third phase of the Battle of the Somme 1916)

The Battle of Guillemont (fourth phase of the Battle of the Somme)

The Battle of Flers-Courcelette (sixth phase of the Battle of the Somme 1916)

The Battle of Morval (seventh phase of the Battle of the Somme 1916)

The Battle of Le Transloy (eighth phase of the Battle of the Somme 1916)

The German Retreat to the Hindenburg Line

The Battle of Langemarck (second phase of Third Battle of Ypres)

The Battle of the Menin Road (third phase of the Third Battle of Ypres)

The Battle of the Polygon Wood (fourth phase of the Third Battle of Ypres)

The Battle of Cambrai

The Battle of St Quentin (first phase of the First Battles of the Somme 1918)

The Actions at the Somme Crossings (first phase of the First Battles of the Somme 1918)

The Battle of Rosieres (third phase of the First Battles of the Somme 1918)

The Division was withdrawn after the heavy fighting of the Somme battles, moving on 20th April 1918 to an area south west of Amiens. During the summer months it received many new drafts of men, and from October 1918 it took part in the general advance that resulted in victory.

Demobilisation began in January 1919, and was completed in May. Since first moving to Fance four years previously, the Division had suffered 35,470 casualties.

59th Brigade

10th (Service) Bn, the King's Royal Rifle Corps (joined September 1914, disbanded February 1918)

11th (Service) Bn, the King's Royal Rifle Corps (joined September 1914)

10th (Service) Bn, the Rifle Brigade (joined September 1914, disbanded February 1918)

11th (Service) Bn, the Rifle Brigade (joined September 1914)

2nd Bn, the Cameronians (Scottish Rifles) (joined February 1918)

59th Brigade Machine Gun Company (joined on 3 March 1916, left 15 March 1918)

59th Trench Mortar Battery (formed by 16 July 1916)

60th Brigade

6th (Service) Bn, the Ox & Bucks (joined September 1914, disbanded February 1918)

6th (Service) Bn, the KSLI (joined September 1914)

12th (Service) Bn, the King's Royal Rifle Corps (joined September 1914)

12th (Service) Bn, the Rifle Brigade (joined September 1914)

60th Brigade Machine Gun Company (joined on 3 March 1916, left 15 March 1918)

60th Trench Mortar Battery (formed by 16 July 1916)

61st Brigade

7th (Service) Bn, the Somerset Light Infantry (joined September 1914)

7th (Service) Bn, the DCLI (joined September 1914)

7th (Service) Bn, the KOYLI (joined September 1914, disbanded February 1918)

11th (Service) Bn, the Durham Light Infantry (joined September 1914, left to become Divisional Pioneers January 1915)

12th (Service) Bn, the King's (Liverpool) (joined January 1915)

61st Brigade Machine Gun Company (joined on 3 March 1916, left 15 March 1918)

61st Trench Mortar Battery (formed by 16 July 1916)

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Divisional Troops

12th (Service) Bn, the King's (Liverpool) (joined September 1914, left for 61st Brigade January 1915)

9th (Service) Bn, the Devons (joined August 1914, left April 1915)

11th (Service) Bn (Pioneers), the Durham Light Infantry (joined from 61st Brigade, January 1915)

217 Company MGC (joined March 1917, merged into Divisional MG Battalion, March 1918)

20 Battalion MGC (formed March 1918)

14 Motor Machine-Gun Battery (joined by 26 January 1915, left for 1 ANZAC 22 April 1916))

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Divisional Mounted Troops

HQ, D Squadron and MG Section, 1/1st Westmoreland and Cumberland Yeomanry (joined by 24 June 1915, left for 2nd Cavalry Division 29 April 1916)

20th Divisional Cyclist Company (formed 22 December 1914, left for XIV Corps 17 May 1916)

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Divisional Artillery

XC Brigade RFA (broken up 30 August 1916)

XCI Brigade RFA

XCII (Howitzer) Brigade RFA (left to became an Army Brigade, 8 January 1917)

XCIII Brigade RFA

20th Heavy Battery RGA (raised for the Division, but left August 1915 and moved to France)

20th Divisional Ammunition Column

V.20 Heavy Trench Mortar Battery RFA (formed by 24 May 1916, broken up on 2 February 1918, men transferred to XXII Corps HTMB)

X.20, Y.20 and Z.20 Medium Mortar Batteries RFA (jformed by 24 May 1916; on 2February 1918, Z broken up and batteries reorganised to have 6 x 6-inch weapons each)

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Companies of the RE

83rd Field Company

84th Field Company

96th Field Company (joined from 26th Division, January 1915)

20th Divisional Signal Company

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Field Ambulances of the RAMC

60th Field Ambulance (joined October 1914)

61st Field Ambulance (joined October 1914)

62nd Field Ambulance (joined October 1914)

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20th Divisional Train ASC (158, 159, 160, 161 Coys ASC joined October 1914)

33rd Sanitary Section (joined in England, left for Fourth Army Area 24 April 1917)

20th Division Motor Ambulance Workshop (joined 22 June 1915, disbanded and men transferred to Divisional Supply Column, 31 March 1916)

221st Divisional Employment Company (formed 30 June 1917)

32nd Mobile Veterinary Section AVC