Operation Dexterity (16 December 1943-10 February 1944) was the Allied invasion of western New Britain, carried out in order to secure the straits between New Britain and New Guinea, and to tighten the Allied net around the Japanese base at Rabaul.
There were two important areas on New Britain. The first was the major Japanese base of Rabaul, at the northern tip of the island, with a network of airfields and strong defences. The Allies knew that they would have to neutralise Rabaul before they could safely move on to the west. The second were the Dampier and Vitiaz Straits, which passed the southern tip of the island. The Dampier Strait runs between New Britain and the smaller island of Umboi (or Rooke), and the Vitiaz Strait between Umboi and the northern shore of New Guinea. The Allies needed to have control of these straits before they could safely advance further west along the north coast of New Guinea, on their road back to the Philippines.
The Allies decided that it wasn't worth the cost of a direct assault on Rabaul. Instead they would surround it with a string of more easily captured bases and use air power to prevent the Japanese from using Rabaul as an offensive base.
In contrast the Japanese had to be cleared from the western tip of the island. The key location was Cape Gloucester, on the north-western tip of the island. Control of this area would prevent the Japanese from attacking Allied shipping in the straits, while an airfield here could be used to support attacks further along the coast of New Guinea and for attacks on Rabaul (in the long run the Cape Gloucester airfield would prove to be rather disappointing, and was soon reduced to emergency status only).
The original plan for Dexterity was for two initial attacks - one at Cape Gloucester on the north-west corner of the island and one at Lindenhafen Plantation on the south coast. The northern force would then advance east to Talasea, on the Willaumez Peninsula, while the southern force would capture the Japanese base at Gasmata. The advance would then stop at the Talasea-Gasmata line. The attack on Gasmata was cancelled during the planning stage, partly because the terrain was known to be very swampy and partly because the invasion fleet would be exposed to attack from Rabaul.
The invasion began on 15 December when US troops under General Julian Cunningham landed at Arawe. They quickly established control over the Arawe Peninsula, and prepared to fight off any Japanese counterattack.
On 26 December the 1st Marine Division (General William Rupertus) made the main landings, at Cape Gloucester. The Japanese made a major effort to stop this landing, sending waves of up to 80 aircraft from Rabaul. The American fighter screen, mainly made up of P-38 Lightings, fought off these attacks, and by the end of December the air attacks stopped.
On the night of 27-28 December the Japanese launched a counterattack against the beachhead at Borgen Bay, but were repulsed with heavy losses.
On 28 December the Japanese launched the first of two attacks on the American positions at Arawe, but were repulsed. The same day saw the Marines at Cape Gloucester push past a strong defensive position with twelve bunkers, using their tanks to destroy the Japanese positions.
On 29 December the Japanese made a second attack on the Arawe position, and suffered very heavy losses. That evening a fresh infantry battalion arrived, but Major Komori decided to stay on the defensive.
On the same day the Americans captured the airfield at Cape Gloucester without encountering any serious resistance. The Japanese counterattacked in strength on 30 December, but this attack was a costly failure and the airfield area was now secured.
The next target in the Cape Gloucester area was Hill 660, a key position about two miles south of Borgen Bay, from where the Japanese could hit the airfield with artillery fire. It took two weeks to get into position to attack this hill, which was protected by a series of steep sided ridges. After an artillery bombardment on 12 January the Marines attacked on 13 January, but were repulsed. A second attack on 14 January was more successful, and the Japanese were forced off the top of the hill.
On 16 January 1944 the Americans carried out a successful attack at Arawe, advancing 1,600 yards with the help of light tanks. This ended the fighting on the Arawa front. Major Komori withdrew to defend the airfield, before in February he was ordered to retreat further east. On the same day the Japanese launched a counterattack against Hill 660, but were repulsed with heavy losses. Both of the original landing areas were now secured.
For the rest of January and all of February the Marines slowly advanced along the north coast of New Britain. In mid-February this advance forced the Japanese to order Major Komori to retreat from the Arawe area.
Umboi Island, in the straits, was also occupied in this period, after an unopposed landing on 12 February. Soon after this the Japanese decided to abandon the western half of the island, and on 23 February the troops in the west were ordered to retreat back to Rabaul.
On 10 February General Krueger declared that Operation Dexterity was over, but this didn’t mark the real end of the fighting on New Britain.
The eventual American target was the airfield at Talasea and the Willaumez Peninsula. The 5th Marines reached the Willaumez Peninsula on 5 March, and on the following day they carried out an amphibious assault on Talasea, landing at Volupai Plantation, on the west coast of the Peninsula. The area was secured within three days - Talasea Airfield was captured on 8 March - and after that the pace of the fighting began to die down. The Americans had no intention of advancing any further. The Japanese had over 100,000 men at Rabaul, at the far end of the island, but they had lost control of the seas around the island and the land routes were too difficult for them to carry out any sizable counterattack. The Marines spent several weeks carrying out low level patrols, before they were finally replaced by the US Army's 40th Division at the end of April. The Army captured Hoskins Plantation on 7 May, and then settled down to a pattern of patrols.
By the time the fighting died down the Marines had lost 310 dead and 1,083 wounded. The Japanese calculated their own losses as 3,868 dead.
By the summer of 1944 the fighting had largely died down. The Americans held the western end of the island, and the Japanese the eastern end. Neither side was interested in provoking the other, so the interior was largely left alone. The main allied presence consisted of native patrols led by Australian officers.
By this point most of the Japanese were based in a defensive position around Rabaul, in the north-eastern part of the Gazelle Peninsula. They had a major post at Henry Reid Bay, at the eastern side of the neck of land connecting the Gazelle Peninsula to the rest of New Britain, and a series of outposts that spread another 150 miles along the west coast to Montagu Bay.
In the spring of 1944 Captain B. Fairfax-Ross, commander of the Australian led native forces on the south coast was given the task of clearing the coast as far as Henry Reid Bay. The Allies had already taken some positions within this area and had a base inland at Lakiri, but Fairfax-Ross was still badly outnumbered by his opponents. He did have some support from the Americans, and in June an American patrol pushed the Japanese out of Awul at the western end of their line of posts.
Most activity in this period took place around Wide Bay, a larger bay that contained Henry Reid Bay within in it. Fairfax-Ross decided to make this area his main target, while the Japanese were also active in the area. On the night of 17-18 July Allied aircraft hit the Japanese base at Milim, at the southern end of Wide Bay. The Japanese left some men at a new base a little to the west, but most of their forces pulled back north to the Gazelle Peninsula. August saw the last Japanese outposts west of Wide Bay on the south coast eliminated, and in early September the Australians began to work on a new base at Jacquinot Base, on the approaches to Wide Bay. The same month also saw an Australian patrol penetrate quite some way onto the north coast of the Gazelle Peninsula, helping to improve the intelligence picture.
Milim fell to the Australians in September despite the failure of an air attack. The Japanese retreated to Waitavalo, on Henry Reid Bay but then launched a series of counterattacks. By the end of the month they had retaken Milim, and had 700 men in the area, but they were forced to retreat again after heavy air attacks on 6-8 October. This ended the period of guerrilla warfare, and Fairfox-Ross was ordered to focus on intelligence gathering instead, ready to support the 5th Division.
In November 1944 the Australian 5th Division replaced the US 40th Division on New Britain. The Australians decided to conduct a limited offensive against the Japanese, who they mistakenly believed to be only 35,000 strong. The 6th Brigade landed at the new base at Jacquinot Bay on 4 November, while other parts of the division replaced the Americans further west. The 6th Brigade soon expanded east, and on 28-28 December two companies landed at Sampun, at the southern tip of Wide Bay.
The 36th Battalion took over the base at Cape Hoskins, the easternmost American base on the north coast. General Ramsey, commander of the division, had orders to maintain 'fighting spirit' of his men and to limit any Japanese movement out of the Gazelle Peninsula.
The next eastern movement came on the north coast. In November and December the Japanese were active on the coast west of the Gazelle Peninsula. After some clashes with the Australians they withdrew from the area, and on 13 January 1945 the 36th Battalion began to move east to Ea Ea, at the western end of Open Bay (the equivalent of Wide Bay on the north coast). The battalion then sent patrols east, and clashed with similar Japanese forces of the coast of Open Bay. A period of minor clashes around the bay ended in early April when the Japanese withdrew to the Turiu River, north of Open Bay, and protected by a band of swamps. The Australians advanced to Watu, at the western end of Open Bay, and paused.
Between 26 January and 11 February the 6th Brigade on the south coast established a new base at Milim, and began to patrol towards Henry Reid Bay. The Australians then moved up towards the new Japanese positions near Kamandram Mission towards the head of Wide Bay. The two forces clashed on 11 February, but the Australians continued to advance. Their new orders were to hold the Waitavolo-Tol area at the northern side of Henry Reid Bay. This order triggered six weeks of heavy fighting, which began on 5 March and saw the Australians clear the Japanese out of a series of strong defensive positions.
At the end of this period the Australians had captured the neck of the Gazelle Peninsula. For the next four months they limited themselves to patrolling with the odd clash with small Japanese patrols. The Australian orders forbade them from advancing too far to the north-east, while the Japanese were happy to stay put around Rabaul. By this point the Japanese commanders at Rabaul had realised that the Allies weren't going to attack, and put some effort into dragging Allied reinforcements into the area, but without success.
This was effectively the position when news of the end of the war arrived on 15 August. When the Japanese surrendered they still had 16,200 naval troops, 53,200 soldiers and 20,000 civilian workers at Rabaul, with another 11,100 troops and 1,200 soldiers on New Ireland. In total they had 101,700 personnel on the two islands when they surrendered.