On 27 August 1943, the
172nd Infantry Regiment, forming part of the
43rd Infantry Division (assigned to Major General
Oscar Griswold's
XIV Corps), crossed Hathorn Sound via the Diamond Narrows and landed unopposed on the southeastern coast of the island. After establishing a
beachhead, the landing forces sent out patrols to locate the Japanese. They then split into two forces that advanced north up the eastern and western coasts through dense jungle and mangrove swamps towards Stima Lagoon in the east and Bustling Point in the west. The advance was slow, held up by the terrain and fatigue. The first clash occurred on 1 September on the eastern coast, south of the lagoon. During the initial stages of the battle, the defending Japanese troops 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 173rd Infantry Regiment had previously fought on the mainland around Munda and Baanga. It was understrength, and its troops were fatigued and affected by
malaria. In an effort to cut off the Japanese line of withdrawal, the 2nd Battalion, 173rd Infantry landed near the lagoon and dispatched more troops to reinforce the eastern patrols. Meanwhile, on the western side of the island, the 1st Battalion embarked on several landing craft and traversed the Wana Wana Lagoon to link up with the patrol that had reached Bustling Point without establishing contact with the Japanese. From there, they established a beachhead around the western part of the Bomboe Peninsula. On 5 September, the 2nd Battalion attacked heavily fortified Japanese positions around Stima Lagoon that were defended with mines,
booby traps, and machine guns. Supported by artillery batteries firing from Kolombangara, the Japanese resistance proved more intense than US planners had anticipated, and so the 3rd Battalion, 173rd Infantry Regiment was also landed around the lagoon to assist on 5 September. Having expected only limited combat, the fighting to secure Arundel eventually evolved into a major operation, and the 173rd Infantry Regiment was initially reinforced by the
169th around 8 September. This regiment relieved the 1st Battalion, 173rd Infantry around Bustling Point, allowing the battalion to move to the east coast to support the regiment's other two battalions around Stima Lagoon. To break the deadlock, other reinforcements were sent later, with US forces reaching a peak strength of eight infantry battalions. These were drawn from various units including the
27th Infantry Regiment (a Regular Army regiment detached from the
25th Infantry Division) and a company from the
103rd Infantry Regiment, along with 4.2-inch mortars from the
82nd Chemical Battalion, two
batteries of 155 mm
howitzers, a reconnaissance troop, and 13 US Marine tanks (a
platoon from each of the
9th,10th, and 11th Defense Battalions). The 27th was landed around the Bomboe Peninsula—where the 169th Infantry had established a blocking position—with artillery support from the mortars and 155 mm guns, while other artillery from the 9th 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 the island, dispatching a battalion of Colonel Satoshi Tomonari's
13th Infantry Regiment commencing 8 September, with orders to secure food by attacking US troops around Munda or Bairoko on New Georgia. They were also charged with delaying the US forces long enough to enable elements of the
8th Combined Special Naval Landing Force and the
South Seas Detachment to withdraw from Kolombangara. Two battalions of the US 27th Infantry Regiment arrived around Bustling Point on 10–11 September; while the 1st Battalion remained at Enogai on northern New Georgia. Their commander, Colonel Douglas Sugg, would assume command of all US troops in the north of the island. The 27th was tasked with clearing Sagekarasa Island and the Bomboe Peninsula, attacking towards the east in an effort to push the Japanese back towards the blocking positions that the 172nd Infantry Regiment was holding. US troops from the 169th Infantry Regiment secured the Bustling Point area around 12 September, and then elements the 27th Infantry advanced along the narrow neck of the Bomboe Peninsula. Other elements of the 27th Infantry crossed over to Sagekarasa Island, wading ashore and forcing the Japanese in the area to withdraw from the western part of the island. The 172nd also pushed 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 beachhead in the west. In response, over the course of the next two nights, the Japanese began evacuating their westernmost staging area and made preparations to reinforce their shrinking perimeter with the remainder of the 13th Infantry Regiment. While crossing from Kolombangara via 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, the reinforcements launched a frenzied counterattack, and although this was eventually contained by elements of the 27th, 169th and 172nd Infantry Regiments, 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 Marine tanks, which arrived on the Bomboe Peninsula via landing craft from Munda. He began a series of coordinated assaults utilizing the tanks to provide close support to his infantry. The fighting continued for another week as the Japanese were forced into a small perimeter on the Stima Peninsula. Exploiting the sound of a heavy downpour to muffle the noise of their engines, five tanks from the 11th Defense Battalion moved into position behind the 27th on the west coast on the night of 16–17 September. The following morning the five tanks, operating in two waves with infantry support, destroyed a Japanese strongpoint, allowing the front line to advance . There were no losses amongst the tanks during this first engagement, but the following day Japanese defenders firing 37 mm guns destroyed two tanks, which 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 from all three defense battalions took part in the 27th Infantry Regiment's attack on the pocket of Japanese resistance on the Stima Peninsula. Using their 37 mm guns to fire into the jungle, they attacked northwards in two waves to provide mutual support. Defending Japanese troops attempted to swarm over the tanks to attach magnetic mines to them, but infantrymen operating alongside the tanks shot them down, while snipers were used to harass the Japanese antitank gunners and prevent them from firing on the tanks. The US Navy cut off the Japanese supply line, so on 20–21 September the Japanese evacuated Gizo and Arundel, withdrawing back to Kolombangara via barge. In order to cover their withdrawal, the Japanese laid down an intense artillery bombardment from Kolombangara, which prevented the surrounding US troops from attacking the withdrawing troops; meanwhile, US gunners and mortarmen maintained their own bombardment on the withdrawing Japanese barges. Some Japanese who attempted to swim across to Kolombangara drowned in the attempt and were found washed up on the shore in the aftermath. ==Aftermath==