The 12th Battalion was raised in Bristol in August 1914 by the Citizen's Recruiting Committee. It was taken over by the War Office in June 1915 and left for France in November as part of the 95th Brigade in the 5th Division. The battalion went into action in 1916 during the Somme offensive: on 29 July at Longueval during the Battle of Delville Wood; between 3 and 5 September during the Battle of Guillemont, in which it suffered some 300 casualties; and on 25 September during the Battle of Morval. On 8 May 1917, during the Battle of Arras, the battalion was practically annihilated with the loss of 296 men at Fresnoy, and it did not see action again until 4 October in the Battle of Broodseinde. In December, the 5th Division was transferred to Italy, where it went into the line along the River Piave, but the battalion saw little action beyond patrolling. The division returned to France in April 1918, occupying positions in the line near Nieppe Forest, and the battalion saw action on 25 April and 28 June, both times successfully advancing the front line. Its last action came during the Second Battle of Bapaume, where it suffered some 100 casualties on 21 August but succeeded in capturing Irles on 23 August. On 6 October, the battalion was disbanded and its men distributed among the other units of the 5th Division.