The Battle of Rabaul, also known by the Japanese as Operation R, an instigating action of the New Guinea campaign, was fought on the island of New Britain in the Australian Territory of New Guinea, from 23 January into February 1942. It was a strategically significant defeat of Allied forces by Japan in the Pacific campaign of World War II, with the Japanese invasion force quickly overwhelming the small Australian garrison, the majority of which was either killed or captured. Hostilities on the neighbouring island of New Ireland are usually considered to be part of the same battle. Rabaul was significant because of its proximity to the Japanese territory of the Caroline Islands, site of a major Imperial Japanese Navy base on Truk.