When did Papua New Guinea come under Australian rule?

During WWI,Papua New Guinea was occupied by Australian troops to defend the British half. When the Treaty of Versailles was established after World War I, Australia administered German New Guinea (the northern half), and the British part of the island came to be considered an External Territory of the Commonwealth of Australia, though it was still "owned" by Britain. At this point, the southern half came under Australian rule. The two territories were regarded as separate territories, known as 'Papua' and 'New Guinea'.

After the New Guinea Campaign of World War II, the two territories came together as 'Papua New Guinea'. Australia still administered Papua New Guinea until the country was granted full independence on 16 September 1975.