When the First World War broke out, the 3rd Battle Squadron was assigned to the Grand Fleet, with "Dominion" conducting operations as part of the Northern Patrol. Through 1914 and 1915, the ships frequently went to sea to search for German vessels, but "Britannia" saw no action during this period. By the end of the year, the Grand Fleet stopped operating with the older 3rd Battle Squadron ships, and in 1916, the squadron was detached to the Nore Command. The unit subsequently dissolved in March 1918. She was a depot ship for the raids on Zeebrugge and Ostend, and, decommissioned in May, ended the war as an accommodation ship. She was sold in 1921 and eventually scrapped in 1924.