During World War II Manus Island was the site of an observation post manned by No. 4 Section, 'B' Platoon, 1st Independent Company, Australian Imperial Force., who also provided medical treatment to the inhabitants. Manus was first bombed by the Japanese on 25 January 1942, the radio mast being the main target. On 8 April 1942 an Imperial Japanese force consisting of the light cruiser Tatsuta, destroyer Mutsuki and a troop transport ship Mishima Maru entered Lorengau harbour, and several hundreds of Japanese soldiers of the 8th Special Base Force, swarmed ashore onto Australia's mandated responsibility. With little and limited resources the Australian 4th section withdrew to the jungle. The Japanese established an administrative base and airstrip. In February 1944 the United States and Australian forces launched a six-week campaign to recapture the facility, which was eventually achieved on 18 March 1944.
The Americans expanded the Japanese base and constructed a huge naval base at nearby Lombrum. An airstrip capable of handling heavy bombers was constructed at Momote and it was here that the invasion to capture the Philippines was staged.
After the war the base was scrapped and all equipment was bulldozed into pits or the harbour.