"Locust" remained part of the Seventh Patrol Flotilla in August 1914, which transferred to the Humber on the East coast of England following the outbreak of the First World War. In November 1914, "Locust" was transferred to Scapa Flow, where she carried out local patrol and escort duties. "Locust" remained part of the Scapa Flow local patrol forces until January 1918, but transferred to the Firth of Forth as part of the Methil Convoy Flotilla by February that year. By May 1918, "Locust" had moved again, returning to the Seventh Flotilla based on the Humber, remaining there until the end of the war.