The battle of Arundel Island (27 August-20 September 1943) was both part of the mopping up operations after the fall of Munda on New Georgia, and of the operations to isolate the remaining Japanese base on Kolombangara.
Arundel Island is at the southern end of the Kula Gulf, between New Georgia and Kolombangara. Before the fall of Munda the Japanese had only used it as a barge staging post, but it now gained greatly in importance. Both sides realised that it was a valuable defensive outpost for the Japanese base at Kolombangara - if it fell into American hands the airfield at Vila on Kolombangara would come within range of their artillery. The Japanese also saw it as a useful evacuation point for troops still trying to escape from New Georgia. On 20-22 August they evacuated the troops still defending Baanga Island over to Arundel.
At dawn on 27 August the 172nd Infantry, 43rd Division, crossed from New Georgia to the southern end of Arundel Island. This regiment had already taken part in the fighting at Munda and the battle on Baanga Island, and was already tired. At this stage the island was only defended by around 200 men, but the Japanese could easily reinforce it from Kolombangara. As the Americans moved north Japanese resistance stiffened.
After the unopposed landing the invasion force formed two reinforced companies and sent one up the east coast and one up the west coast.
The main fighting took part at the northern end of the island. The north coast has a somewhat unusual layout, with two long narrow gulfs running into the land from the west. The north-western point on the main landmass was at Bustling Point. The first of these gulfs then separated the main island from the long Bomboe Peninsula, which ran from west to east, joining the north coast about half way along. A second narrow gulf began at this point, bordered in the north by Sagekarasa Island and the Stima Peninsula. The coast then curved around to the south towards Stima Lagoon.
The first Japanese troops were found by the eastern patrol on 1 September, south of Stima Lagoon. At this stage resistance was limited and the patrol was able to continue its advance, but the 2nd Battalion of the 172nd Regiment was landed at Stima Lagoon to support their advance. At the same time the 1st Battalion of the 172nd Regiment was moved up the west coast to join the western patrol group at Bustling Point. The 1st Battalion sent some troops across the gulf to the western tip of the Bomboe Peninsula. The 27th Infantry Regiment soon took over that position while a battalion of the 169th took over at Bustling Point. This allowed the entire 172nd Regiment to concentrate on the east coast.
On 5 September the 2nd Battalion of the 172nd Regiment launched an attack north at Stima Lagoon, but the Americans had finally found the main Japanese defensive positions and this attack was stopped dead.
On 8 September both sides committed fresh troops to the fighting on Arundel Island. The Americans moved one battalion from the 169th Infantry onto the island, while the Japanese moved the 3rd Battalion, 13th Infantry Regiment. Sasaki was seriously considering launching a counterattack against the Americans at Munda, using Arundel as a launch pad. The US 169th Infantry took over the beachhead on the north-western coast, allowing the 1st Battalion of the 172nd to move to the east coast.
On 12 September the 27th Infantry began a slow advance east along the Bomboe Peninsula, an attack that saw the first combat use of the new 105mm mortars. This was a slow advance, but the Japanese were constantly pushed back, and by 13 September the Americans were close to the eastern end of the peninsula. On 13 September a second battalion from the 27th Infantry swam across to Sagekarasa Island, where they held off a series of desperate Japanese counterattacks.
By 14 September the Japanese troops on Kolombangara had been isolated and were beginning to run short of food. Sasaki's situation had deteriorated to the point where his plans moved from a possible counterattack to a raid for food. The rest of the 13th Infantry was moved across to Arundel, and plans were prepared for a raid on Munda or Bairoko. At this stage the Japanese only really held the Stima Peninsula, and that foothold was being pressured by the US 27th Infantry in the west and the 172nd Infantry in the south.
On 15 September the Japanese attempted to expand their foothold on the island by launching a fanatical attack on the American lines. The 172nd and 27th Infantry, reinforced by the 169th, managed to hold their lines, although the Japanese came close to success in some places.
By now the Japanese High Command had decided to abandon the central Solomons and focus on Bougainville. This news didn’t reach Sasaki until 15 September, and he was now faced with the task of evacuating 12,435 men from Kolombangara and Arundel. The troops on Arundel were ordered to carry out a delaying action while the evacuation was prepared.
On 16 September the Americans moved fresh troops onto the island, including thirteen Marine Corps tanks. Some of these tanks were used to support a 27th Infantry attack on the Bomboe Peninsula on 17 September and managed to push the Japanese out of their positions. A second attack on the 18th was less effective and two of the tanks were knocked out. All of the available tanks were used in a more successful attack on 19 September, and the Japanese perimeter began to crumble.
The Japanese retreat began on the night of 19-20 September. On the morning of 20 September the American troops on Sagekarasa discovered that their opponents were gone, and on 21 September the troops on Arundel made the same discovery. The battle for Arundel Island was over. It had cost the Americans 44 dead and 256 wounded, while the Japanese had lost 500 dead in the defensive battle. Kolombangara had already been bypassed by the American invasion of Vella Lavella and at the end of September the Japanese began to evacuate their last base in the New Georgia islands.