In answer to Lord Kitchener's appeal, in late August and September 1914 many men joined Alexandra's Princess of Wales's Own Yorkshire Regiment, better known as The Green Howards. Recruits came from around the Middlesbrough area and the ironstone mines on the North Yorkshire moors, while others came from the East Durham coalfield and the Durham City area.

The 8th and 9th Battalions left the Regimental Depot in Richmond in late September and moved to Frensham on the Hampshire/Surrey border, where they trained hard until bad weather forced a move to barracks in Aldershot.

They arrived on the Somme front at the end of June 1916, but were not involved in the fighting until 5 July, when the 9th Battalion captured Horseshoe trench and Lieutenant Donald Simpson Bell won the VC when he destroyed a German machine gun position. On 10 July both battalions took part in the capture of Contalmaison, a village that had been a first day objective. A second VC was awarded posthumously to Private William Short of the 8th Battalion during the fighting in Munster Alley in August 1916.

The next year found the 23rd Division in the Ypres Salient, where they were in and out of the line until June 1917 when they took part in the Battle of Messines and the 8th Battalion had the honor of taking Hill 60.

In November 1917 the division was sent to Italy to bolster the hard-pressed Italian Army, but the 9th Battalion returned to France in 1918 where they fought until the Armistice. The 8th Battalion stayed on in Italy and fought at the crossing of the Piave and Vittorio Veneto, which brought the war to an end in Italy.