15th (Prince of Wales's Own Civil Service Rifles) Battalion, The London Regiment, a Territorial unit and had their headquarters at Somerset House when war broke out in August 1914, serving as part of 4th London Brigade, 2nd London Division. The Division had just arrived for their annual summer camp on Salisbury Plain when war was declared in August 1914, they were at once recalled to their home base and mobilised for war service. The Division concentrated in the St Albans area for training, with the 15th Battalion at Bedmond, and then moving to billets at Watford in November. They proceeded to France on the 18th of March 1915, landing at le Havre, being only the second TF Division to arrive in theatre.