HMS Lancaster was one of 10 Monmouth-class armoured cruisers built for the Royal Navy in the first decade of the 20th century. Upon completion she was assigned to the 3rd Cruiser Squadron of the Mediterranean Fleet. She remained there until 1912 when she returned home to be placed in reserve. The ship was recommissioned in 1913 for service with the 4th Cruiser Squadron on the North America and West Indies Station. She remained there until she was assigned to the Grand Fleet in 1915. She was transferred to the Pacific in 1916 and she became flagship of the Eastern Squadron in 1918. The ship was sold for scrap in 1920.