The 'Battle of Arundel Island' was fought between US and Japanese forces for control of Arundel island, part of the New Georgia group of the Solomon island group, within 'Toenails' (27 August/11 September 1943).

The battle took place toward the end of the 'Toenails' campaign after the capture of Munda airfield and mopping-up operations in western New Georgia had led to the Japanese evacuation of mainland New Georgia. The US command decided to occupy the island so that it could be used as a base for artillery to fire on the main Japanese troop concentration on Kolombangara island, just to the north-west of New Georgia.

After landing on the south-eastern tip of Arundel island, the single three-battalion US infantry regiment initially allocated to the operation undertook a two-pronged advance along the eastern and western coasts. The island’s small Japanese garrison was reinforced during the fighting, and offered stiffer resistance than the US forces had expected. As a result, the latter were strongly reinforced by elements of three other infantry regiments, totaling eight infantry battalions, as well as artillery, mortars and US Marine Corps tanks. After heavy fighting, the defending Japanese were pushed into a pocket on the northern coast around the Stima peninsula, from which they were evacuated by barge to Kolombangara on 20/21 September.

Measuring some 10 miles (16 km) in length on its north-western/south-eastern axis and 6 miles (9.6 km) in width, Arundel island lies off the western coast of New Georgia island, separated by a narrow body of water consisting of Hathorn Sound and the Diamond Narrows. It is situated to the south of Kolombangara, from which it is separated by the Blackett Strait, and lies in the mouth of the point at which the Kula Gulf enters the Solomon Sea, from which it is shielded farther to the west by Wana Wana island. The island of Gizo lies farther to the west in the Vella Gulf. To the west and north-west lie Vonavona island and the Ferguson Passage respectively. Round Hill, with a height of 250 ft (76 m), is located in the southern part of the island.

From 30 June 1943, US forces had begun operations to secure the New Georgia islands, as part of their 'Cartwheel' advance toward the main Japanese base around Rabaul on New Britain island. The primary US objective on New Georgia was the seizure of Munda airfield on the north-western coast of the island so that it could be used to support subsequent Allied operations. After the airfield had been taken early in August, Japanese troops had begun an evacuation of mainland New Georgia, while US troops undertook mopping-up operations.

The bulk of the Japanese forces had been withdrawn to Kolombangara by the middle of August. During the next phase of their advance, the Allies had decided to bypass this concentration and land instead on Vella Lavella island in 'Dogeared', which began on 15 August. Meanwhile, the final stages of Allied operations to secure western New Georgia saw US forces secure Baanga islet between 11 and 21 August. With Baanga captured, mopping-up operations secured the area of New Georgia north from Munda to Bairoko. The Japanese command considered launching a counterattack on New Georgia at this time, using troops on Kolombangara. Efforts to bring forward reinforcements early in August had been disrupted by the loss of three destroyers during the 'Battle of Vella Gulf', and consequently these plans were cancelled and it was decided to relocate the troops from Baanga to Arundel, from where they could delay further Allied advances. This move was completed on 22 August.

Possession of Arundel Island offered control of the Blackett Strait, which stretches to the north from New Georgia, as well as the Diamond Narrows to the south. It also offered firing points on either Munda for the the Japanese and on Villa for the Americans. In the wake of the campaign on the mainland, Allied commanders decided to capture Arundel island so that it could be used to shell the main Japanese troop concentration on Kolombangara, most especially the airfield in the Villa area. Before the invasion, the island was held by 200 Japanese of the 229^th Regiment, under the overall command of Lieutenant General Minoru Sasaki. US planners anticipated only a minor operation to secure the island, and therefore made the initial assignment of only a single infantry regiment to the task.

On 27 August, the 172^nd Infantry, which was an element of Major General John R. Hodge’s 43^rd Division in Major General Oscar W. Griswold’s XIV Corps, crossed Hathorn Sound via the Diamond Narrows and landed unopposed on Arundel’s south-eastern coast. After establishing a beach-head, the landing force despatched patrols to locate the Japanese. It then divided into two forces that advanced north up the eastern and western coasts through dense jungle and mangrove swamps toward Stima Lagoon in the east and Bustling Point in the west. The advance was slow as a result of the inhospitable terrain and fatigue among the US soldiers. The first clash occurred on 1 September on the eastern coast in the area to the south of the lagoon. In the battle’s early stages, the defending Japanese sought to engage the attacking US troops from maximum range, or conduct harassing raids on static points, while generally avoiding contact to prevent being decisively engaged.

The 173^rd Infantry had previously fought on the mainland around Munda and Baanga. It was therefore understrength and its men tired and affected by malaria. In an effort to cut the Japanese line of withdrawal, the 2/173^rd Infantry was landed near the lagoon and despatched more troops to reinforce the eastern patrols. Meanwhile, on the island’s western side, the 1/173^rd Infantry embarked in a number of landing craft and traversed the Wana Wana Lagoon to link with the patrol that had reached Bustling Point without establishing contact with the Japanese. From there, the US force established a beach-head round the western part of the Bomboe peninsula. On 5 September, the 2/173^rd Infantry attacked heavily fortified Japanese positions around Stima Lagoon that were defended with mines and booby traps, and also by machine guns.

Supported by artillery firing from Kolombangara, the Japanese resistance proved more intense than US planners had anticipated and on 5 September the 3/173^rd Infantry was landed around the lagoon to assist. The fighting to secure Arundel island eventually evolved into a major operation in which the 173^rd Infantry was initially reinforced by the 169^th Infantry around 8 September. This latter regiment relieved the 1/173^rd Infantry around Bustling Point, allowing the battalion to move to the eastern coast to support the regiment’s other two battalions around Stima Lagoon. To break the deadlock, other reinforcements were sent at a later date, and the US forces reached a peak strength of eight infantry battalions. These were drawn from a number of units, including the 27^th Infantry (a regular regiment detached from the 25^th Division) and one company of the 103^rd Infantry, together with with 4.2-in (106.7-mm) heavy mortars of the 82^nd Chemical Battalion, two batteries of 155-mm (6.1-in) howitzers, one reconnaissance troop, and 13 US Marine tanks in the form of a platoon each of the 9^th,10^th and 11^th Defense Battalions. The 27^th Infantry was landed around the Bomboe Peninsula, where the 169^th Infantry had established a blocking position, with artillery support from the mortars and 155-mm (6.1-in) guns, while other artillery of the 9^th Defense Battalion based on mainland New Georgia around Munda Point fired against Japanese guns on Kolombagara to support the eastern force.

Meanwhile, the Japanese also reinforced their strength on the island, despatching one battalion of Colonel Satoshi Tomonari’s 13^th Regiment from 8 September, with orders to secure food by attacking US troops around Munda or Bairoko on the New Georgia mainland. The regiment was also charged with delaying the US forces long enough to enable elements of the 8^th Combined Special Naval Landing Force and the Nanto Detachment to withdraw from Kolombangara. Two battalions of the 27^th Infantry arrived around Bustling Point on 10/11 September, and the 1/27^th Regiment remained at Enogai on the northern end of New Georgia. The regimental commander, Colonel Douglas Sugg, assumed command of all US troops in the north part of Arundel island. The 27^th Infantry was tasked with clearing Sagekarasa island and the Bomboe peninsula, attacking toward the east in an effort to push the Japanese back toward the blocking positions which the 172^nd Infantry was holding.

Men of the 169^th Infantry secured the Bustling Point area on about 12 September, and then elements the 27^th Infantry advanced along the narrow neck of the Bomboe peninsula. Other elements of the 27^th Infantry crossed to Sagekarasa island, wading ashore and forcing the Japanese in the area to withdraw from the island’s western part. The 172^nd Infantry also pushed to the north on the eastern coast, squeezing the Japanese defenders against the two forces. On the evening of 12/13 September, the Japanese launched several local counterattacks, but these failed to dislodge the US beach-head in the west. Over the course of the next two nights, the Japanese began to evacuate their westernmost staging area and made preparations to reinforce their shrinking perimeter with the remainder of the 13^th Regiment. While crossing from Kolombangara by barge on 14/15 September, the Japanese reinforcements came under heavy US artillery fire, resulting in the deaths of Tomonari and two of his battalion commanders. Despite these losses, however, the reinforcements launched a frenzied counterattack, and although this was eventually contained by elements of the 27^th, 169^th and 172^nd Infantry, it brought the US advance to a halt again. The Japanese subsequently resumed delaying tactics.

In an effort to reinvigorate the offensive, Sugg arrived on Arundel on 15 September to oversee a renewed attack supported by the US Marines' tanks, which arrived on the Bomboe peninsula via landing craft from Munda. Sugg began a series of co-ordinated assaults making use of the tanks to provide close support to his infantry. The fighting continued for another week as the Japanese were driven into a small perimeter on the Stima peninsula. Exploiting the sound of a heavy downpour to muffle the noise of their engines, five tanks of the 11^th Defense Battalion moved into position behind the 27^th Infantry on the western coast during the night of 16/17 September. On the following morning the five tanks, operating in two waves with infantry support, destroyed a Japanese strongpoint, allowing the front line to advance 500 yards (455 m). There were no losses among the tanks during this first engagement, but on the following day Japanese defenders used 37-mm guns to destroy two tanks that had become isolated from infantry support after adopting the wrong formation. The crews were rescued from their vehicles, though, as the supporting infantry recovered from their initial surprise and laid down supporting fire.

On 19 September, 11 tanks of all three defense battalions took part in the 27^th Infantry’s attack on the pocket of Japanese resistance on the Stima peninsula. Using their 37-mm guns to fire into the jungle, the tanks attacked northward in two waves to provide mutual support. The Japanese defenders attempted to swarm over the tanks and attach magnetic mines, but infantrymen operating alongside the tanks shot them down, while snipers were used to harass the Japanese anti-tank gunners and prevent them from firing on the tanks.

Unable to receive supplies as a result of the interdiction of their sea lanes of communication by the US Navy, on 20/21 September the Japanese evacuated Gizo and Arundel islands, withdrawing to Kolombangara by barge. In order to cover their withdrawal, the Japanese laid down an intense artillery bombardment from Kolombangara, and this prevented the surrounding US troops from attacking the withdrawing troops; meanwhile, US gunners and mortarmen maintained their own bombardment of the withdrawing Japanese barges. Some Japanese who attempted to swim across to Kolombangara drowned in the attempt.

US losses in the 'Battle of Arundel Island' amounted to 44 men killed and 256 wounded, while the Japanese lost 345 men killed and 500 wounded. Minor mopping-up operations on the island continued after 21 September. As a result of the capture of Arundel island, US commanders had managed to secure the air base around Munda from counterattack or shelling, although it remained under threat from Japanese air attack. In the aftermath, the 'Dogeared' fighting continued on Vella Lavella, where the New Zealand 14^th Brigade arrived to assume responsibility for the final advance through the coastal areas.

Meanwhile, the Japanese decided to evacuate more than 12,000 troops from Kolombangara as part of a major retrograde operation in the Solomon islands group. The evacuation was conducted over the course of several nights by barge, starting on 28/29 September and continuing to 2/3 October. The Japanese then evacuated Vella Lavella on 6/7 October, bringing the New Georgia campaign to a conclusion. During the evacuation operations, the US Navy claimed to have sunk up to 46 barges, killing several thousand Japanese troops, but ultimately the Japanese evacuation was successful. The delay inflicted by the defenders on Arundel island allowed the Japanese to improve their defences around Rabaul and on Bougainville island: many of the troops evacuated from Kolombangara were involved in the 'Cherryblossom' fighting on Bougainville later in the war. The next phase of the Allied advance through the Pacific would see them land at Cape Torokina in November 1943 as part of efforts to secure Bougainville, while further actions were undertaken by the New Zealanders in the Treasury Islands and the US Marines on Choiseul.