This is a list of Northumberland Fusiliers battalions in World War I. When the First World War broke out in August 1914, the Northumberland Fusiliers, a fusilier infantry regiment of the British Army, consisted of 7 battalions, eventually expanding to 52 battalions, although not all existed at the same time, of which 29 served overseas. It was the second largest infantry regiment of the British Army during World War I, surpassed only by the 88 battalions of the London Regiment.