The 4th Battalion (Bn) came into being as a result of the Army reforms of 1908, when ‘Volunteer’ and Yeomanry Bns were combined to form a new organisation called the Territorial Force. Battalion Headquarters were established in Hexham and detachments were formed along Tynedale at Bellingham, Corbridge, Haltwhistle, Hayden Bridge, Newburn and Prudhoe.

The 4th Bn was one of four Northumberland Fusilier Territorial Bns, all of whom were mobilised when war broke out on the 4th of August 1914. The following day, 17 officers and 660 men from the 4th Bn reported to the war station and embarked on a period of intensive training in Newcastle and later the Blyth area. The 4th Bn sailed for France, as an integral part of the Northumbrian (Territorial) Division, on the 20th of April 1915.

Within a week the 4th Bn was committed to action in the Ypres Salient, suffering heavy casualties in an assault on the German front line during the Battle of St Julien. Over the next three years the Bn fought in most of the British sectors on the Western Front including the Somme, Passchendaele, Arras, the Lys and Aisne. Casualties were typically heavy, with more than 770 fusiliers killed and 2000 wounded, necessitating hundreds of men to be recruited and drafted, primarily from Tynedale during the early months of the war, but eventually from all over the United Kingdom.

The 4th Bn virtually ceased to exist after the Battle of the Aisne (27 May 1918), because so many fusiliers were killed, wounded or captured.