The 'Battle of Rabaul' was the heart of the Japanese 'R' operation to take the islands of New Britain and New Ireland, and was fought between Japanese and Australian troops as the first stage of the Japanese undertaking that started the New Guinea campaign (23 January/February 1942).

Though small on overall scope, the 'Battle of Rabaul' was a strategically significant defeat of Allied forces by Japan in the Pacific campaign of World War II: the Japanese invasion force quickly overwhelmed the small Australian garrison, most of whose men were either killed or taken prisoner. 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 group, the location of a major Imperial Japanese navy base on the island of Truk.

Following their seizure of the town, the Japanese forces turned Rabaul into a major base and proceeded to land on mainland New Guinea, advancing toward Port Moresby on the south coast of Papua toward the south-eastern tip of New Guinea. Heavy fighting followed along the Kokoda Track (or Trail) and around Milne Bay before the Japanese were eventually pushed back toward Buna and Gona in North-East New Guinea by a time early in 1943. As part of 'Cartwheel', throughout 1943/45 Allied forces later sought to isolate the Japanese garrison on Rabaul, rather than to capture it, using air power as their predominant weapon, with US and Australian ground forces pursuing a limited campaign in western New Britain during this time.

By the end of the war, there was still a sizeable garrison at Rabaul, with large quantities of equipment that were subsequently abandoned. In the aftermath, it took the Allies more than two years to repatriate the Japanese soldiers who had surrendered, while clean-up efforts continued past the late 1950s. Many relics including ships, aircraft and weapons, as well as abandoned positions and tunnels, remain in the area.

Rabaul lies on the north-eastern end of the island of New Britain. At the time of the battle, the town was the capital of the Australian-administered Territory of New Guinea, having been captured from the Germans in 1914. In March 1941, the Australians dispatched a small garrison to the region as tensions with Japan heightened. The small Australian army garrison in New Britain was based on Lieutenant Colonel Howard Carr’s 700-strong 2/22^nd Battalion, an Australian Imperial Force infantry battalion. This battalion formed part of 'Lark' Force, which eventually numbered 1,400 men under the command of Lieutenant Colonel John Scanlan. The force also included personnel of a local militia unit, the New Guinea Volunteer Rifles, a coast-defence battery, an anti-aircraft battery, an anti-tank battery and a detachment of the 2/10^th Field Ambulance. A commando unit, the 130-strong 2/1^st Independent Company, was detached to garrison the nearby island of New Ireland.

In 1941, the Allies had planned to expand Rabaul into a secure fleet anchorage with a radar station and a strong defensive minefield, but these plans were ultimately shelved as the Allied planners decided that they did not have the capacity to expand the garrison around Rabaul, nor was the naval situation conducive to its reinforcement should the garrison come under attack. Nevertheless, the decision was made that the garrison would remain in place to hold Rabaul as a forward observation post. The main tasks of the garrison were protection of Vunakanau, the main Royal Australian Air Force 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 only 10 lightly armed CAC Wirraway single-engined training aircraft and four Lockheed Hudson twin-engined light bombers of No. 24 Squadron.

For the Japanese, as noted above, Rabaul was important because of its proximity to the Caroline islands group, which was the site of a major Imperial Japanese navy base on Truk island. The capture of New Britain offered the Japanese a deep-water harbour and airfields to provide protection to Truk and also to interdict Allied lines of communication between the USA and Australia. Following its capture of Guam in the Mariana islands group, Major General Tomitaro Horii’s South Seas Detachment was tasked with the seizure of Kavieng and Rabaul as part of 'R'.

The Japanese planning began with air reconnaissance of Rabaul in an effort to fix the deployment of the defending troops. Flown from Guam to Truk, Japanese planners determined three possible schemes of manoeuvre based on these dispositions: a landing near Kokop, aimed at establishing a beach-head; a landing on the north coast of Rabaul, followed by a drive on Rabaul from behind the main defences; and a multi-pronged landing focused on capturing the airfields and centre of the town. The planners eventually settled upon the third option. For the invasion, the Japanese established a brigade group based on Lieutenant General Hiroshi Takeuchi’s 55^th Division. Its main combat units were the 144^th Regiment, which comprised a headquarters unit, three infantry battalions, one artillery company, one signals unit, and one munitions squad, as well as a few platoons of the 55^th Cavalry Regiment, one battalion of the 55^th Mountain Artillery Regiment and one company of the 55^th Engineer Regiment. These forces would be supported by a large naval task force, and landing operations would be preceded by a heavy air campaign to destroy the Allied air assets in region and thereby prevent them from interfering with the landing operations.

Most male civilians were forced to stay in Rabaul, but females unnecessary to the defence of the base were evacuated in December 1941, shortly before the start of the Japanese air raids. Starting on 4 January 1942, Rabaul came under attack by large numbers of Japanese carrierborne aircraft. After the odds facing the Australians mounted significantly, the RAAF commander signalled RAAF headquarters in Melbourne with the Latin saying 'Nos Morituri Te Salutamus' ('we who are about to die salute you'). On 14 January, the Japanese assault force embarked at Truk and began to make the passage to Rabaul as part of a naval task force, which consisted of two fleet carriers (Kaga and Akagi, seven cruisers, 14 destroyers and numerous smaller vessels and submarines under the command of Vice Admiral Shigeyoshi Inoue. On 20 January, more than 100 Japanese aircraft attacked Rabaul in several waves. Eight Wirraway aircraft rose to attack them, and in the combat which followed three RAAF aircraft 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 coast artillery was destroyed and the Australian infantrymen were withdrawn from Rabaul itself. On the following day, an Consolidated Catalina twin-engined flying boat of the RAAF located the invasion fleet off Kavieng, and its crew managed to send a signal before the 'boat was shot down.

As the Australian ground troops took up position along the western shore of Blanche Bay where they prepared to meet the landing, the remaining RAAF elements, comprising two Wirraway and one Hudson aircraft, were withdrawn to Lae in North-East New Guinea. Once the aircraft had departed, carrying a number of wounded, the Australians destroyed the airfield. The Japanese bombing continued around Rabaul on 22 January, and early on the morning of that day a Japanese force of between 3,000 and 4,000 men landed just off New Ireland and waded ashore in deep water rendered more dangerous by the presence of mud pools. The 2/1^st 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 Detachment entered Simpson Harbour and about 5,000 troops, mainly of the 144^th Regiment under the command of Colonel Masao Kusunose, began to land on New Britain.

There followed a series of desperate actions near the beaches round Simpson Harbour, Keravia Bay and Raluana Point as the Australians attempted to drive back the attack. The 3/144^th Regiment, under the command of Lieutenant Colonel Kuwada Ishiro, was checked at Vulcan Beach by a mixed company of Australians from the 2/22^nd Battalion and the New Guinea Volunteer Rifles, but elsewhere the other two battalions of the South Seas Detachment were able to land at unguarded locations and begin to move inland. Within hours, Lakunai airfield had fallen to the Japanese. Assessing the situation as hopeless, Scanlan ordered 'every man for himself', and Australian soldiers and civilians split into small groups, up to the size of a company, and retreated through the jungle, moving along the northern and southern coasts. During the fighting on 23 January, the Australians lost two officers and 26 other ranks killed.

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, Lerew insisted that they be evacuated and organised for them to be flown out by flying boat and his one remaining Hudson. In the days following the capture of Rabaul, the Japanese began mopping-up operations from 24 January. 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, the men’s health and military effectiveness declined rapidly. Leaflets posted by Japanese patrols or dropped from the air stated in English that 'You can find neither food nor way of escape in this island and you will only die of hunger unless you surrender.' Horii tasked the 3/144^th Regiment with searching the southern part of the Gazelle peninsula and killing or capturing the remaining Australians. More than 1,000 Australian soldiers were captured or surrendered during the following weeks after the Japanese had landed a force at Gasmata, on New Britain’s southern coast, during 9 February, severing the Australians' line of retreat. Following this, the Japanese reorganised their forces, occupying a line along the Keravat river, to prevent possible counterattacks.

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. Notwithstanding these efforts, Allied losses, particularly among personnel captured, were very high and casualties during the fighting for Rabaul early in 1942 were heavily in favour of the Japanese. The Allies lost six aircrew killed and five wounded, along with 28 soldiers killed and more than 1,000 taken prisoner. Against this, the Japanese lost only 16 men killed and 49 wounded.

Of the more than 1,000 Australian soldiers taken prisoner, about 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, other Australian prisoners were shot. The Allies later placed responsibility for the incident on Kusunose, commanding officer of the 144^th Regiment, but late in 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 7,267-ton Montevideo Maru, in which they were being transported from Rabaul to Japan, was sunk off the northern coast of Luzon island in the Philippine islands group by the US submarine Sturgeon.

According to one Japanese historian, the operation to capture Rabaul was the only undertaking of the New Guinea campaign that was wholly successful. Following their capture of Rabaul, the Japanese quickly repaired the damage to the town’s airfield and Rabaul became the largest and most important Japanese base in New Guinea, and the linchpin of the Japanese defence of the region. The Australians tried to restrict Rabaul’s development soon after its capture by means of a bombing counterattack in March. The Japanese eventually extended their control across New Britain, establishing airfields at Cape Gloucester on the island’s western tip and several small outposts along the coast to provide stop-over points for small craft and barges travelling between Rabaul and New Guinea. Meanwhile, a handful of 'Lark' Force men 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 coastwatchers to provide information about Japanese shipping movements.

For the Japanese, the capture of Rabaul was followed with further operations on mainland New Guinea, beginning with 'Sr' to capture the area of Salamaua and Lae in the Huon Gulf beginning in March 1942. Throughout this same year and into a time early in 1943, the Allies and Japanese fought along the Kokoda Track, at Milne Bay against the Japanese 'Re', and around Buna and Gona as the Japanese sought to advance to the south toward Port Moresby. By the middle of 1943, the tide had turned in favour of the Allies, who began a grand strategic offensive in the South-West Pacific and South Pacific Areas to advance north-westward through the Solomon islands group and New Guinea. By a time late in November 1943 the Japanese force in Rabaul had been reduced by air power, including a large raid mounted from the aircraft carriers Saratoga and Princeton on 5 November. It is believed that after this occasion, no Japanese heavy ships ever came to Rabaul.

Allied planners had considered the recapture of Rabaul, but eventually settled on isolating and bypassing it as part of 'Cartwheel'. In December 1943, US marines and army troops landed in western New Britain at Arawe and Cape Gloucester in 'Director' and 'Backhander' respectively. Subsequent Allied operations on New Britain gradually restricted the Japanese to the area around Rabaul. In November 1944, the Australians returned to the island when advanced elements of Major General A. H. Ramsay’s 5^th Division landed at Jacquinot Bay on the south coast, and relieved Major General Rapp Brush’s US 40^th Division. The Australians then conducted a number of other landings around the island’s coast as they conducted a limited advance to the 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, there were still around 69,000 Japanese troops in Rabaul.

Large quantities of equipment were subsequently abandoned around Rabaul after the war, and it took more than two years for the Allies to repatriate the Japanese garrison taken prisoner at the time of Japan’s surrender. In the late 1950s, Japanese companies began to salvage many of the wrecked ships around Rabaul, but many abandoned positions, tunnels and equipment, such as aircraft and weapons, can still be found in the area.