The ship became part of the Grand Fleet when it was formed shortly after the beginning of the First World War in August 1914. Aside from participating in the Battle of Jutland in May 1916, and the inconclusive action of 19 August several months later, her service during the war generally consisted of routine patrols and training in the North Sea. "Neptune" was deemed obsolete after the war and was reduced to reserve before being sold for scrap in 1922 and subsequently broken up.