'R' was the Japanese seizure of Rabaul on New Britain in an operation parallel with the 'O' seizure of Kavieng on New Ireland, the two major islands of the group lying to the north of the great island of New Guinea’s eastern tip (23 January 1942).

New Britain is the largest of the islands of the Bismarck archipelago. It is about 325 miles (520 km) long and between 20 and 90 miles (32 and 145 km) wide, and possesses an area of 14,100 sq miles (36520 km²). The island lies to the north-east of New Guinea and the north-west of the Solomon islands group, and shares with these a heavily jungled terrain. There is a superb anchorage at Simpson Harbour on the north-eastern tip of the island, which late in 1941 possessed modest docking facilities at Rabaul, as well as two airfields. The Gazelle peninsula on which Rabaul is located was the only part of the island with a road network or any other significant development. In addition to the two airfields near Rabaul, there were grass airstrips at Gasmata, Arawe and Talasea on the eastern side of Willaumez peninsula on the north coast.

As well as being jungle-clad, the island is rugged, with a central mountain range along most of its length and reaching a maximum altitude of 7,999 ft (2438 m) at Mt Sinewit. The range includes several active or dormant volcanoes, of which 'The Father' (Mt Ulawan) is the highest at 7,657 ft (2334 m).

The anchorage at Rabaul is a flooded caldera, and resurgent domes in the harbour area emit quantities of steam and ash from time to time. Sulphurous fumes greatly reduced the habitability of the many underground fortifications which the Japanese built in this area during their occupation. Much of the coast was backed by swamps, and although there are numerous beaches suitable for landing, most of the coast is fringed with reefs. In 1940 the indigenous population was estimated at 101,000, and the number of Europeans and Asians at 4,674.

Rabaul was a primary target in the Japanese 'Centrifugal Offensive' tide of expansion up to April 1942 , for it offered an excellent land-locked harbour as a base for Vice Admiral Shigeyoshi Inoue’s 4^th Fleet tasked with the defence of the central sector of Japan’s southern defensive perimeter. New Britain had also been identified since September 1941 as the long-term headquarters of General Hitoshi Imamura’s 8^th Area Army to control the Japanese army forces in New Guinea and in the Solomon islands group.

The envisaged defence perimeter was to run south through the central Pacific and then turn to the west in the Ellice islands group, the southern sector taking in the western end of the Solomon islands group, the southern portion of Papua and all of New Guinea, and the islands of Timor and Java before turning to the north-west toward the Malay Barrier. Together with the nearby Admiralty islands group, New Britain and New Ireland were ideal base areas for the completion of the southern sector as the large harbour at Rabaul was backed by a smaller harbour at Kavieng, and the two islands could rapidly be developed with airfields for the long-range bombers on which both the Japanese army and Japanese navy depended for far-flung operations in the Pacific.

The Japanese fully recognised Rabaul’s importance in their planning for the 'Centrifugal Offensive', for its proximity to the Caroline islands group, the location of a major naval base at Truk atoll. The capture of New Britain offered the Japanese a deep-water harbour and airfields to provide outer protection for Truk and also to interdict the Allied maritime lines of communication between the east coast of the USA and Australia.

The final plan for the seizure of Rabaul was formulated on 3 January 1942 in a meeting at Truk between Inoue and Major General Tomitaro Horii, commander of the South Seas Detachment. Following its 'G' capture of Guam, this had been allocated the task of taking Kavieng and Rabaul: a brigade group based on the 55^th Division, the South Seas Detachment had as its main combat units the 144^th Regiment (headquarters unit, three infantry battalions, one artillery company, one signals unit, and one munitions squad) 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.

The first Japanese air raid on Rabaul was launched from Truk on the following day. Although coast watcher Cornelius L. Page on Tabar was able to give a warning of the first raid, by 16 Mitsubishi G3M 'Nell' medium bombers of the 'Chitose' Kokutai, the Australian anti-aircraft fire could not reach their altitude, and the Commonwealth Wirraway aircraft of No. 24 Squadron were launched too late and, in any event, lacked the speed to catch the bombers. The Japanese in turn were very inaccurate with their bombing. A second raid by 11 Kawanishi H6K 'Mavis' flying boats of the 'Yokohama' Kokutai at dusk also bombed inaccurately. Repeat raids on 6 and 7 January were more accurate, destroying or damaging most of the Australian aircraft on the ground.

A reconnaissance flight over Truk on 9 January revealed a large concentration of Japanese shipping in the anchorage. However, Japanese raids did not resume until 16 January, when another pair of raids by G3M and H6K warplanes suggested that the invasion was imminent. In fact, the invasion group had sailed from the island of Guam in the Mariana islands group two days earlier, and a powerful covering force sailed from Truk on the following day. For reasons that have never been explained, orders were issued from Canberra that Norwegian freighter Herstein at Rabaul was to continue to load copra and that there was to be no evacuation of civilians.

New Britain’s garrison of 1,400 Australian troops, commanded by Lieutenant Colonel John J. Scanlan, included a mere 716 first-line soldiers, in the shape of the 2/22^nd Battalion, deployed from March 1941 as fear of war with Japan increased, as 'Lark' Force. The force also included personnel from a local militia unit, the New Guinea Volunteer Rifles, one coast defence battery with two 6-in (152-mm) guns, one anti-aircraft battery with two guns of which one had a cracked breech, one light anti-tank battery, and a detachment of the 2/10^th Field Ambulance. The main tasks of the garrison were protection of the Royal Australian Air Force airfield at Vunakanau and the flying boat anchorage, which were important in the surveillance of Japanese movements in the region. However, the RAAF contingent had little offensive capability at Rabaul, for it comprised just 10 lightly armed Wirraway training aircraft and four Lockheed Hudson light bombers of No. 24 Squadron. A commando unit, the 130-man 2/1^st Independent Company, was detached to garrison the nearby island of New Ireland.

As noted above, from January 1942 the defences of the two islands, especially their artillery, were softened up by land-based Japanese aircraft operating from Truk in the Caroline islands group, the main base of Admiral Isoroku Yamamoto’s Combined Fleet, before the assault force arrived and landed with little opposition.

On 14 January the Rear Admiral Kiyohide Shima’s 19^th Minelaying Division had departed Guam for Rabaul with the minelayers Okinoshima, Tenyo Maru and Tsugaru, destroyers Mochizuki and Mutsuki (30^th Destroyer Division), auxiliary gunboats Kongo Maru and Nikkai Maru, and a number of army transports with the 144^th Regiment of Horii’s South Seas Detachment. On 17 January Rear Admiral Sadamichi Kajioka arrived from Truk to meet Shima’s force with the light cruiser Yunagi, destroyers Asanagi, Oite and Yunagi (29^th Destroyer Division) and Yayoi (30^th Destroyer Division), one auxiliary and two transports with elements of the 2^nd Maizuru Special Naval Landing Force embarked and the aircraft depot ship Hijirigawa Maru.

Cover and support for 'R' were provided by Vice Admiral Chuichi Nagumo’s 1^st Carrier Air Fleet with the fleet carriers Akagi and Kaga (1^st Carrier Squadron) and Shokaku and Zuikaku (5^th Carrier Squadron), battleships Hiei and Kirishima (1/3^rd Battleship Squadron), heavy cruiser Chikuma (8^th Cruiser Squadron) and the 1^st Destroyer Flotilla with the light cruiser Abukuma and destroyers Isokaze, Hamakaze, Kasumi, Arare, Kagero, Shiranui and Akigumo. Nagumo’s force departed Truk on 17 January for the seas to the north of New Ireland.

On 18 January Rear Admiral Aritomo Goto’s 6^th Cruiser Squadron followed with the heavy cruisers Aoba, Kinugasa, Kako and Furutaka, and on 20 January the invasion force left for Kavieng with Rear Admiral Mitsuharu Matsuyama’s 18^th Cruiser Squadron comprising the light cruisers Tatsuta and Tenryu, destroyers Kikuzuki, Uzuki and Yuzuki (23^rd Destroyer Division) and a number of transports carrying the rest of the 2n Maizuru Special Naval Landing Force and the whole of the Kashima Special Naval Landing Force.

On 20 January the carrier force made a heavy attack on Rabaul using 18 Mitsubishi A6M Reisen 'Zero' fighters, 45 Nakajima B5N 'Kate' level bombers and 28 Aichi D3A 'Val' dive-bombers in several waves. Eight Wirraway aircraft attacked the Japanese attackers, and in the battle which resulted three Australian aircraft were shot down, two crash-landed and another was damaged; six Australian aircrew were killed in action and another five wounded. One of the bombers was shot down by anti-aircraft fire, but Herstein was wrecked and the collier Westralia was sunk.

As a result of the air attacks, the Australian infantry force was withdrawn from Rabaul itself to take up positions along the west coast of Blanche Bay, where it was believed the landing would take place.

On the following day, a Consolidated Catalina flying boat of the Royal Australian Air Force located the Japanese invasion fleet off Kavieng, and its crew managed to send a signal before being shot down.

On 24 February the remaining Hudson flew out with wounded men. A second raid on 22 January destroyed the coastal battery, and the remnants of No. 24 Squadron were evacuated to the south coast in whatever vehicles were available before eventually being evacuated by flying boat.

On 21 January, while the 1^st Carrier Squadron remained to the north of New Ireland, the 5^th Carrier Squadron had meanwhile steamed with Chikuma and three destroyers into the Bismarck Sea, where the 6^th Cruiser Squadron was also taking up a position to cover the landings. The boats of Rear Admiral Shinzo Onishi’s 7^th Submarine Flotilla, based on the tender Jingei, patrolled off St George’s Channel to cover the Rabaul operation using Ro-61, Ro-62, Ro-63, Ro-64, Ro-65, Ro-67 and Ro-68.

The bombing of the area round Rabaul continued on 22 January, and early in the morning of that day the first 500 men of a Japanese force which quickly reached something between 3,000 and 4,000 troops landed just off New Ireland and waded ashore in deep water filled with dangerous mudpools. 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 Australians fell back towards the Sook river.

After the destroyers had refuelled on 21 January, and with air support from the carriers, during the night of 22/23 January the invasion fleet approached Rabaul and before dawn on 23 January, the ships carrying the South Seas Detachment entered Simpson Harbour, and a force of some 5,000 men, mainly of the 144^th Regiment, began to land on New Britain under the command of Colonel Masao Kusunose.

There followed a series of desperate actions near the beaches around Simpson Harbour, Keravia Bay and Raluana Point as the Australians attempted to turn back the attack. The 3/144^th Regiment, under the command of Lieutenant Colonel Kuwada Ishiro, was held up at Vulcan Beach by a mixed company of Australians of 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 moving inland. Within hours, Lakunai airfield had been captured by the Japanese, and once Scanlan had ordered 'every man for himself', 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. Though he had initially been ordered to turn his ground staff into infantrymen in a last-ditch effort to defend the island, the senior air force officer insisted that they be evacuated, and organised for them to be flown out by flying boat and the 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, the men’s health and military capability declined rapidly. Leaflets posted by Japanese patrols or dropped from the air stated, in English, that they could find neither food nor any way of escape in this island and they would only die of hunger unless they surrendered.

Horii tasked the 3/144^th Regiment to search the southern part of the Gazelle peninsula and capture the remaining Australians. Some 1,049 Australian soldiers were captured or surrendered during the following weeks after the Japanese had landed a cut-off force at Gasmata, on New Britain’s south coast, on 9 February, thereby severing the Australians' line of retreat toward New Guinea. From the New Guinea mainland, some civilians and individual officers of 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. The Australians tried to restrict the development of the airfield soon after its capture by means of a bombing attack in March.

A handful of 'Lark' Force personnel remained at large on New Britain and, working with members of the indigenous population, undertook guerrilla operations against the Japanese, serving mainly as coast watchers and providing information of Japanese shipping movements.

Of the 1,049 Australian prisoners of war, 158 were massacred on or about 4 February 1942 in four separate incidents around Tol and Waitavalo. Six men survived these killings and later described to a court of inquiry what had happened. The Allies later placed responsibility for the incident on Kusunose, commander of the 144^th Regiment, but late in 1946 he starved himself to death before he could be placed on trial.

At least 800 soldiers and 200 civilian prisoners of war, most of them Australian, lost their lives on 1 July when Montevideo Maru, the ship in which they were being transported from Rabaul to Japan, was sunk off the north coast of Luzon in the Philippine islands group by the US submarine Sturgeon.

After their defeat of the Australian garrison of New Britain, the Japanese soon brought Rabaul into full operation as a naval and air base for softening-up operations in New Guinea and Papua, the targets for 'Rs', while longer-term plans were implemented for the defence of the islands, which the Japanese saw as the ideal bastion against any Allied offensive toward the Philippine islands group from the south, and as the perfect outer defence for Truk. Thus the Japanese subsequently developed Rabaul into their most important base in the South-West Pacific.

Lakunai was ready to receive fighters by 25 January and medium bombers by mid-February. The Japanese eventually made Vunakanau their main airfield and completed new airfields at Rapopo on the coast 14 miles (23 km) to the south-east of the town in December 1942; Tobera inland of Rapopo in August 1943; and Keravat on the north coast 13 miles (21 km) to the south-west of the town. Keravat suffered from such poor drainage that it was all but abandoned by the Japanese, but the other four airfields were modern facilities with all-weather concrete runways and revetments for 80 to 120 aircraft each (totalling 265 fighter and 166 bomber revetments for the Rabaul area.) Vunakanau eventually had a runway 5,200 ft (1585 m) long by 135 ft (41 m) wide paved with 4 in (100 mm) of concrete. Rapopo had a runway 4,350 ft (1325 m) long on ground cleared by army tanks and prisoners of war as there were no bulldozers available.

Rabaul itself tripled in size during the occupation, Japanese engineers building more than 600 structures with an aggregate floor space of 2.8 million sq ft (260120 m²) using drafted local labour and the the output of 29 sawmills. The road network was expanded by 395 miles (635 km), 23 Diesel power stations with a capacity of about 1 MW were installed, and 13 new wells were drilled with a capacity of 290,000 US gal (1.098 million litres) per day.

The Japanese garrison eventually numbered 100,000 men with tanks and artillery. The anti-aircraft defences totalled 367 guns, including almost 100 75- and 80-mm (2.95- and 3.15-in) weapons, 24 120-mm (4.72-in) dual-purpose guns, about 100 25-mm cannon and about 120 heavy machine guns. The defences also included 43 coast-defence guns, of which 37 were of 120-mm (4.72-in) calibre or greater. Other fixed defences included about 240 heavy guns and howitzers, about 240 field and anti-tank guns, 23 heavy mortars, and 6,000 machine guns and grenade launchers. Early warning was provided by two Type 1 Model 1 radar sets at Tomavatur Mission and nine Type 1 Model 2 radar sets at other locations on New Britain and the surrounding islands. The warning network typically provided a warning of about one hour.

Rabaul became the focus of 'Cartwheel', the first major Allied counter-offensive of the war in the South-West Pacific Area. This began with small probing raids staged through Port Moresby from northern Australia, and over the next two years the air counter-offensive grew in intensity until the fortress was isolated and smashed from the air. However, the base remained in Japanese hands throughout the war as the Allies decided to bypass Rabaul and Kavieng and leave them to 'wither on the vine' as the cost of their seizure would, by the beginning of 1944, exceed their strategic value.