The Territorials in Dorset trace their origins to the 1st Administrative Battalion, Dorsetshire Rifle Volunteers formed at Dorchester.

[2] Eventually in 1880 as a result of the Childers Reforms the regiment was re-designated to the 1st Dorsetshire Rifle Volunteers.

[3][4] The 1st Battalion was stationed in Malta from 1888, in Egypt from 1889, and in British India from 1893, where it took part in operations in the Tirah Campaign on the North West Frontier in 1897–98.

[3][10][11] The 1st Battalion was in Belfast when war broke out: it landed at Le Havre in August 1914 forming part of the 15th Brigade in the 5th Division.

[10][11] The 2nd Battalion was in Poona, India, when war broke out and was shipped, as part of the 16th Indian Brigade, to Mesopotamia, where it was trapped in the Siege of Kut and captured by the Turks.

[10][11] The 5th (Service) Battalion took part in the Gallipoli Campaign, and having been evacuated from there in December 1915, went to Egypt before joining the war on the Western Front in July 1916.

[11] The 6th (Service) Battalion was shipped to Boulogne in France in July 1915 as part of 50th Brigade in the 17th (Northern) Division and saw action on the Western Front.

[10][11] The 3rd (Reserve) Battalion also served in Ireland, at Derry from March 1919, absorbing the 3/4th Bn as postwar demobilisation progressed.

[3][14] In April 1920, during the Anglo-Irish War, soldiers from the regiment fired into a protesting crowd on Bridge Street, leading to riots and skirmishes which saw it fight alongside the Royal Irish Constabulary (RIC) and (later) Ulster Volunteers (UVF) against the Irish Republican Army (IRA).

[18] On 7 February 1920 4th Battalion was reformed in the TF (soon afterwards reorganised as the Territorial Army (TA))with its headquarters in Dorchester and four companies (A–D).

[20] The Officers and Men from the Dorset Regiment who lost their lives while taking part in the suppression of the revolt are commemorated in a brass tablet at the St. Mark's Cathedral, Bangalore.

[b][3][9] The 1st Battalion was a regular army unit and part of the 231st Infantry Brigade, alongside the 1st Hampshires and 2nd Devonshires, for the duration of the war, fighting in Malta between 1940 and 1942, Sicily in August 1943, and Italy in September 1943.