On the outbreak of war on 4 August 1914 the battalion was mobilised at Beverley under the command of Lt-Col Francis Strickland-Constable and moved to its war station at Hedon, near Hull, where the men went into billets and battalion headquarters was established at Holyrood House. Intensive training of reservists and recruits began, with musketry courses fired at Hornsea. From Hedon the battalion despatched its first reinforcement draft (one officer and 95 other ranks) on 25 September to the 1st Battalion fighting on the Aisne, and sent five further drafts in October and November. In December the 2nd Battalion returned from service in India and it also went to France in January 1915. The 3rd Battalion began to supply drafts to this battalion as well. As the prewar reservists and special reservists were used up, the drafts were increasingly made up of wartime recruits and returning wounded. By January 1915 the battalion numbered more than 2000 all ranks.