By 1914, "Hydra" had been withdrawn from active duty to serve as a gunnery training ship. At the outbreak of World War I in at the end of July 1914, Greece's pro-German monarch, Constantine I, decided to remain neutral. The Entente powers landed troops in Salonika in 1915, which was a source of tension between France and Greece. In October 1916, "Hydra" and a pair of torpedo boats defected to the Venizelist faction in the National Schism. Ultimately, the French seized the Greek Navy on 19 October; the heavy units of the Greek fleet were disarmed and placed in reserve for the remainder of the war. "Hydra" was decommissioned in 1918 and stricken from the naval register the next year. She was to be sold for scrapping in 1921, but instead returned to her role as a naval artillery school from 1922 until 1929 when she was broken up for scrap.