Bismarck Archipelago, volcanic island group, 19,200 sq mi (49,730 sq km), SW Pacific, a part of Papua New Guinea. The group includes New Britain (the largest island), New Ireland, the Admiralty Islands, the Mussau Islands, New Hanover, the Vitu Islands, and the Duke of York Islands. The islands are generally mountainous and have several active volcanoes. The chief agricultural products are copra, cacao, coffee, tea, and rubber. Some copper and gold are mined. The inhabitants are mainly Melanesians. Discovered in 1616 by the Dutch explorer Willem Schouten, the group became a German protectorate in 1884. Seized by Australian forces in World War I, the islands were mandated to Australia by the League of Nations in 1920. Japan operated several naval and air bases in the islands during World War II. In 1947, Australia received trusteeship over the group from the United Nations, which were administered as part of the Territory of Papua and New Guinea. The archipelago was included in Papua New Guinea when it established as a self-governing country in 1973.