She was assigned to the 1st Cruiser Squadron of the Channel Fleet upon completion in 1903. She was transferred to the China Station in 1906, and remained there until she returned home in 1913 and was assigned to the reserve Third Fleet. When World War I began in August 1914, the ship was recommissioned and assigned to the 5th Cruiser Squadron in the Central Atlantic to search for German commerce raiders and protect Allied shipping. She was detached upon arrival to patrol the Brazilian coast for German ships, and was later ordered to the South Atlantic to join Rear Admiral Christopher Cradock's squadron in their search for the German East Asia Squadron. He found the German squadron on 1 November off the coast of Chile. The German squadron outnumbered Cradock's force and were individually more powerful; they sank Cradock's two armoured cruisers in the Battle of Coronel. "Monmouth" was lost with all hands.