The Battle of Rabaul, also known by the Japanese as Operation R, was fought on the island of New Britain in the Australian Territory of New Guinea, in January and February 1942. It was a strategically significant defeat of Allied forces by Japan in the Pacific campaign of World War II. Following the capture of the port of Rabaul, Japanese forces turned it into a major base and proceeded to land on mainland New Guinea, advancing toward Port Moresby. Hostilities on the neighbouring island of New Ireland are also usually considered to be part of the same battle. Rabaul was important because of its proximity to the Japanese territory of the Caroline Islands, site of a major Imperial Japanese Navy base on Truk.
The small Australian Army garrison in New Britain—known as Lark Force—numbered 1,400 men and was commanded by Lieutenant Colonel John Scanlan. It included just 716 frontline Australian Imperial Force (AIF) soldiers from the 2/22nd Battalion, deployed from March 1941 as fears of war with Japan increased. The force also included personnel from a local Militia unit, the New Guinea Volunteer Rifles (NGVR), a coastal defence battery, an anti-aircraft battery, an anti-tank battery and a detachment of the 2/10th Field Ambulance. The 2/22nd Battalion Band—which was also included in Lark Force—is perhaps the only military unit ever to have been entirely recruited from the ranks of the Salvation Army. A commando unit, the 130-strong 2/1st Independent Company, was detached to garrison the nearby island of New Ireland.
The main tasks of the garrison were protection of Vunakanau, the main Royal Australian Air Force (RAAF) airfield near Rabaul, and the nearby flying boat anchorage in Simpson Harbour, which were important for the surveillance of Japanese movements in the region. However, the RAAF contingent, under Wing Commander John Lerew, had little offensive capability, with 10 lightly armed CAC Wirraway training aircraft and four Lockheed Hudson light bombers from No. 24 Squadron.
For the Japanese, Rabaul was important because of its proximity to the Caroline Islands, which was the site of a major Imperial Japanese Navy base on Truk. The capture of New Britain offered them a deep water harbour and airfields to provide protection to Truk and also to interdict Allied lines of communication between the United States and Australia. Following the capture of Guam, the South Seas Force, under Major General Tomitaro Horii, was tasked with capturing Kavieng and Rabaul, as part of "Operation R". A brigade group based on the 55th Division, its main combat units were the 144th Infantry Regiment, which consisted of a headquarters unit, three infantry battalions, an artillery company, signals unit, and a munitions squad, as well as a few platoons from the 55th Cavalry Regiment, a battalion from the 55th Mountain Artillery Regiment and a company from the 55th Engineer Regiment. On 14 January, the force embarked at Truk as part of a naval task force, which consisted of two aircraft carriers—Kaga and Akagi—seven cruisers, 14 destroyers, and numerous smaller vessels and submarines under the command of Vice Admiral Shigeyoshi Inoue.
Starting on 4 January 1942, Rabaul came under attack by large numbers of Japanese carrier-based aircraft. After the odds facing the Australians mounted significantly, Lerew signalled RAAF HQ in Melbourne with the Latin motto "Nos Morituri Te Salutamus" ("we who are about to die salute you"), the phrase uttered by gladiators in ancient Rome before entering combat. On 20 January, over 100 Japanese aircraft attacked in multiple waves. Eight Wirraways attacked and in the ensuing fighting three RAAF planes were shot down, two crash-landed, and another was damaged. Six Australian aircrew were killed in action and five wounded. One of the attacking Japanese bombers was shot down by anti-aircraft fire. As a result of the intense air attacks, Australian coastal artillery was destroyed and Australian infantry were withdrawn from Rabaul itself. The following day, an RAAF Catalina flying boat crew located the invasion fleet off Kavieng, and its crew managed to send a signal before being shot down.
As the Australian ground troops took up positions along the western shore of Blanche Bay where they prepared to meet the landing, the remaining RAAF elements, consisting of two Wirraways and one Hudson, were withdrawn to Lae. Once the aircraft had departed with a number of wounded, the Australians destroyed the airfield. The bombing continued around Rabaul on 22 January and early that morning a Japanese force of between 3,000 and 4,000 troops landed just off New Ireland and waded ashore in deep water filled with dangerous mudpools. The 2/1st Independent Company had been dispersed around the island and the Japanese took the main town of Kavieng without opposition; after a sharp fight around the airfield the commandos fell back towards the Sook River. That night, the invasion fleet approached Rabaul and before dawn on 23 January, the South Seas Force entered Simpson Harbour and a force of around 5,000 troops, mainly from the 144th Infantry Regiment, commanded by Colonel Masao Kusunose, began to land on New Britain.
A series of desperate actions followed near the beaches around Simpson Harbour, Keravia Bay and Raluana Point as the Australians attempted to turn back the attack. The 3rd Battalion, 144th Infantry Regiment, under the command of Lieutenant Colonel Kuwada Ishiro, was held up at Vulcan Beach by a mixed company of Australians from the 2/22nd and the NGVR, but elsewhere the other two battalions of the South Seas Force were able to land at unguarded locations and began moving inland. Within hours, Lakunai airfield had been captured by the Japanese force, and Scanlan ordered "every man for himself", and Australian soldiers and civilians split into small groups, up to company size, and retreated through the jungle, moving along the north and south coasts. During the fighting on 23 January, the Australians lost two officers and 26 other ranks killed in action.
Only the RAAF had made evacuation plans. Although initially ordered to turn his ground staff into infantrymen in a last-ditch effort to defend the island, Larew insisted that they be evacuated and organised for them to be flown out by flying boat and his one remaining Hudson. Australian soldiers remained at large in the interior of New Britain for many weeks, but Lark Force had made no preparations for guerrilla warfare on New Britain. Without supplies, their health and military effectiveness declined. Leaflets posted by Japanese patrols or dropped from planes stated in English, "you can find neither food nor way of escape in this island and you will only die of hunger unless you surrender". The Japanese commander, Horii, tasked the 3rd Battalion, 144th Infantry Regiment with searching the southern part of the Gazelle Peninsula and securing the remaining Australians. Over 1,000 Australian soldiers were captured or surrendered during the following weeks after the Japanese landed a force at Gasmata, on New Britain's south coast, on 9 February, severing the Australians' line of retreat.
From mainland New Guinea, some civilians and individual officers from the Australian New Guinea Administrative Unit organised unofficial rescue missions to New Britain, and between March and May about 450 troops and civilians were evacuated by sea. The Japanese quickly repaired the damage to Rabaul's airfield and Rabaul became the biggest Japanese base in New Guinea, and the lynchpin to their defences in the region. The Australians tried to restrict its development soon after its capture by a bombing counter-attack in March. A handful of Lark Force members remained at large on New Britain and New Ireland and, in conjunction with the local islanders, conducted guerrilla operations against the Japanese, serving mainly as coast watchers, providing information of Japanese shipping movements.
Of the over 1,000 Australian soldiers taken prisoner, around 160 were massacred on or about 4 February 1942 in four separate incidents around Tol and Waitavalo. Six men survived these killings and later described what had happened to a Court of Inquiry. The Australian government concluded the prisoners were marched into the jungle near Tol Plantation in small groups and were then bayoneted by Japanese soldiers. At the nearby Waitavalo Plantation, another group of Australian prisoners were shot. The Allies later placed responsibility for the incident on Masao Kusunose, the commanding officer of the 144th Infantry Regiment, but in late 1946 he starved himself to death before he could stand trial. At least 800 soldiers and 200 civilian prisoners of war—most of them Australian—lost their lives on 1 July 1942, when the ship on which they were being transported from Rabaul to Japan, the Montevideo Maru, was sunk off the north coast of Luzon by the U.S. submarine USS Sturgeon.
By late November 1943 the Japanese force in Rabaul had been reduced by airpower, "a hefty part of it on November 5 from Halsey's aircraft carriers Saratoga and Princeton", and "thereafter no Japanese heavy ships ever came to Rabaul." In December 1943, during the Battle of Cape Gloucester, U.S. Marines landed in western New Britain and subsequent Allied operations on New Britain gradually restricted the Japanese force to Rabaul, as part of Operation Cartwheel. In November 1944, the Australians returned to the island when advanced elements of the 5th Division landed at Jacquinot Bay on the south coast, and relieved the US 40th Infantry Division. The Australians then conducted a number of other landings around the island as they conducted a limited advance north, securing a line across the base of the Gazelle Peninsula between Wide Bay and Open Bay. After this, they sought to isolate and contain the main Japanese forces around Rabaul. When Japan surrendered in August 1945, it was found that there were still around 69,000 Japanese troops in Rabaul.