Lüshun (lōˈshŏnˈ) [key], formerly Port Arthur, Jap. Ryojun, former city, SW Liaoning prov., China, at the tip of the Liaodong peninsula. It was formerly combined with Dailian (Dairen) into the joint municipality of Lüda; it now is an adminstrative unit of Dalian. Lüshun is an important naval base dominating the entrance to the Bohai; it is also a southern terminus of the South Liaoning RR. The city was the administrative center of the Liaodong leasehold from 1898 to 1945 (see Liaoning). As a Russian base (1898–1905), it was the site on Feb. 8, 1904, of the surprise Japanese naval attack that precipitated the Russo-Japanese War. The city passed to Japan by the Treaty of Portsmouth (1905). In 1945 it became the headquarters of the Port Arthur Naval Base District under joint Sino-Soviet administration. China regained exclusive control in 1955.