Island group, western Pacific Ocean. Lying northwest of New Guinea, it forms part of Papua New Guinea. It has a total area of about 18,600 sq mi (48,200 sq km); its largest components include New Britain, New Ireland, the Admiralty Islands, and Lavongai (New Hanover). Annexed by Germany in 1884, it was named for Otto von Bismarck. Occupied by Australia in 1914, it was made a mandated territory of Australia in 1920. The group became part of the UN Trust Territory of New Guinea after World War II and part of Papua New Guinea when it attained independence in 1975.
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The first European to visit these islands was Dutch explorer Willem Schouten in 1616.
The islands remained unsettled by western Europeans until they became part of the German protectorate of German New Guinea in 1884. The area was named in honour of the German chancellor Otto von Bismarck.
On 13 March 1888, a volcano erupted on Ritter Island causing a megatsunami. Almost 100% of the volcano fell in to the ocean leaving a small crater lake.
Following the outbreak of World War I, the Australian Naval and Military Expeditionary Force seized the islands in 1914 and Australia later received a League of Nations mandate for the islands. They remained under Australian control — interrupted only by Japanese occupation during World War II — until Papua New Guinea became independent in 1975.