The last Division to be formed for the Third New Army (K3), it began to assemble in the Salisbury Plain area from September 1914. Khaki uniform and equipment were not made available until February-April 1915, and in the meantime eveything was imrovised. Embarkation for France began in September 1915, and the concentration of units at Guignemicourt (west of Amiens) was completed before the end of the month. However, the Division was not destined to remain on the Western Front, because in November 1915 it moved to Salonika, where it then remained. On 2 November, the Division concentrated at Fleselles and moved via Marseilles. On 26 December 1915, units began to move from Lembet to Happy Valley Camp, and all units were in place there by 8 February 1916. The Division took part in the following actions in Salonika:

10-18 August 1916: the Battle of Horseshoe Hill

24-25 April and 8-9 May 1917: the Battle of Doiran

18-19 september 1918: the Battle of Doiran

22-30 September 1918: the Pursuit to the Strumica Valley.

Forward units crossed the Serbian-Bulgarian boundary on 25 September 1918. Hostilities with Bulgaria ceased two days later. The Division advanced towards Adrianople (as the war with Turkey was still underway), but this also soon ceased. 26th Division successively became part of the Army of the Danube and then of the Occupation of Bulgaria. Demobilisation began in February 1919, with Italian troops arriving to replace the dwindling British presence. By 10 May 1919, the Division ceased to exist.

The Division incurred casualties of 8,022 men during the war, a figure much lower than its peers, reflecting the less active front in Macedonia.

77th Brigade

8th (Service) Bn, the Royal Scots Fusiliers (joined October 1914)

11th (Service) Bn, the Cameronians (Scottish Rifles) (joined October 1914)

10th (Service) Bn, the Black Watch (joined September 1914, left 30 June 1918)

12th (Service) Bn, the Argyll & Sutherland Highlanders (joined September 1914)

77th Machine Gun Company, MGC (joined 24 July 1916)

77th Trench Mortar Battery (joined 3 November 1916)

77th SAA Section Ammunition Column (joined 27 July1916)

78th Brigade

9th (Service) Bn, the Gloucesters (joined September 1914, left 4 July 1918)

11th (Service) Bn, the Worcesters (joined September 1914)

7th (Service) Bn, the Ox & Bucks (joined September 1914)

7th (Service) Bn, the Royal Berkshire (joined September 1914)

78th Machine Gun Company, MGC (joined 22 July 1916)

78th Trench Mortar Battery (joined 12 November 1916)

78th SAA Section Ammunition Column (joined 27 July1916)

79th Brigade

10th (Service) Bn, the Devons (joined September 1914)

8th (Service) Bn, the DCLI (joined September 1914)

12th (Service) Bn, the Hampshire (joined October 1914)

7th (Service) Bn, the Wiltshires (joined October 1914, left 16 June 1918)

79th Machine Gun Company, MGC (joined 15 July 1916)

79th Trench Mortar Battery (joined 3 November 1916)

79th SAA Section Ammunition Column (joined 27 July1916)

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Divisional Troops

10th (Service) Bn, the Gloucesters (joined September 1914, left August 1915)

8th (Service) Bn (Pioneers), the Ox & Bucks (joined October 1914, became Pioneers January 1915)

8th (Service) Bn, the Royal Berkshire (joined September 1914, left August 1915)

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Divisional Mounted Troops

A Squadron, the 1/1st Lothians and Border Horse Yeomanry (joined 30 July 1915, left 29 November 1916)

26th Divisional Cyclist Company (formed 4 January 1915, left 16 December 1916)

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Divisional Artillery

CXIV Brigade, RFA (joined September 1914)

CXV Brigade, RFA (joined September 1914)

CXVI Brigade, RFA (joined September 1914)

CXVII Brigade, RFA (joined September 1914, left 9 August 1917 for 74th Division)

XXXI Brigade, RFA (of 28th Division, attached 17 June to 24 August 1917)

LVII Brigade, RFA (joined September 1917)

131st Heavy Battery, RGA (raised for the Division in January 1915 but ordered to move to France, where it joined XXIII HA Brigade on 12 March 1916)

IV Highland Mountain Brigade was briefly attached in August 1918

26th Divisional Ammunition Column (to 22 January 1917, when absorbed into XII Corps AC. This Division retained Brigade AC's to the end)

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Engineer Units

95th Field Company (joined Sep 1914, left 29 January 1915 for 16th (Irish) Division)

96th Field Company (joined Sep 1914, left 1 February 1915 for 20th (Light) Division)

107th Field Company (joined 30 January 1915 from 35th Division)

108th Field Company (joined 30 January 1915 from 35th Division)

131st Field Company (joined 25 April 1915)

26th Divisional Signal Company (joined Sep 1914)

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Field Ambulances of the RAMC

78th (joined 25 August 1915)

79th (joined 25 August 1915)

80th (joined 25 August 1915)

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Other Divisional Troops

26th Divisional Train ASC (202, 203, 204 and 205 Companies ASC joined in November and December 1914 but remained when the Division moved to Salonika, becoming the 32nd Divisional Train. 112, 113, 114 and 115 Coys ASC then transferred from 11th Division. On 22 January 1916, the Train was on board the "Norseman" when it was torpedoed in the Gulk of Salonika, but all personnel were saved, although 600 mules lost their lives. In October 1916 the Train was reorganised into "Pack and Wheel Echelons"; in July 1917 it was further reorganised, to suit local conditions)

38th Mobile Veterinary Section

43rd Sanitary Section (joined 19 August 1915)

38th Mobile Veterinary Section, AVC (joined 18 July 1915)

817th Divisional Employment Company (formed October 1917)

26th Divisional Motor Ambulance Workshop (joined June 1915, but remained in France when the Division moved to Salonika)