On 22 January 1942, the Japanese 8th Area Army invaded the Australian New Guinea Mandate, which consisted of eastern half of Papua New Guinea, the Bismarck Archipelago, and the Solomon Islands. Their immediate objective was the capture of Rabaul, on the northeast tip of New Britain in the Bismarck Archipelago. Rabaul offered a deep water port and secured the southern flank of the main Japanese naval base in the South Pacific, Truk, in the Caroline Islands. On the twenty second, the Japanese 55th Division landed on the island of New Ireland. The next day they assaulted New Britain to capture the port and airfield. They were garrisoned by the 2bn/ 22nd Infantry, an Australian unit recruited almost exclusively from members of the Salvation Army, a battalion of the New Guinea Volunteer Rifles, and a squadron of training aircraft, some light bombers and seaplanes from the Royal Australian Air Force.
For three weeks, the massive waves of Japanese carrier fighters and bombers from Pearl Harbor veterans, Akagi and Kaga, struck Rabaul and the airfield, and swept the skies clear of RAAF resistance. On 23 January as the Japanese were landing, the last Hudson bomber took off for Australia stuffed with wounded. The last obsolete lightly armed trainer had already taken off to attack the invasion force. Before he climbed into his cockpit, the pilot sent a message off to the RAAF HQ: “Nos Morituri Te Salutamus”, the ancient Roman gladiatorial motto, “We who are about to die, salute you.” It was a giant FU for the real and imagined lack of support from the newly formed ABDA Command.
The Australians met the Japanese on the beaches but were thinly spread way, and though they inflicted heavy casualties on the Japanese, were quickly overwhelmed. About 2/3rds of the defenders escaped into the interior of the island from which they conducted guerrilla attacks for many weeks. But long term guerrilla operations were not planned for and no weapons, ammunition, and most importantly medical supplies were stockpiled. The Australians simply died out, or surrendered and were worked to death.
Rabaul became the main Japanese Army and air base for the SouthWest Pacific. The recapture or isolation of Rabaul became the main Allied operational objective in the South Pacific for the next two years. It was from Rabaul that the Japanese conducted the Solomon Islands campaign (started w/ Guadalcanal) and the longest continuous land campaign of the war against the Americans and Aussies: the now mostly forgotten fighting for the island of New Guinea. They were the last obstacles before the Japanese could invade Australia. The brutal fighting for New Guinea and the Solomon Islands continued for the remainder of the war. Amidst their mountainous jungles, these campaigns consumed Allied divisions at a frightening pace and never received the recognition (or supplies) that Nimitz’ Central Pacific and MacArthur’s Philippine’s campaigns received.
Rabaul was never retaken by the Allies during the war.