The 'Battle of the Kula Gulf' was a battle fought between US and Japanese naval forces off the eastern coast of Kolombangara island in the Solomon islands group (6 July 1943).

On the night of 5/6 March 1943, Task Force 68 (four light cruisers and eight destroyers), under the command of Rear Admiral Aaron S. Merrill, was patrolling the Kula Gulf between the islands of Kolombangara and New Georgia when it was informed that a pair of Japanese destroyers had been spotted steaming to the south from the Shortland islands group. At about 22.35 the Japanese ships were detected by radar-equipped 'Black Cat' aircraft (Consolidated PBY Catalina twin-engined flying boats used for nocturnal reconnaissance) scouting for TF68. The Japanese ships were carrying provisions for the airfield at Vila on Kolombangara and successfully unloaded their cargoes before heading northward into the Kula Gulf. The US surface force detected the Japanese destroyers on radar and achieved complete surprise, sinking both ships (Murasame and Minegumo) with gun fire and torpedoes. The US task force then carried out a bombardment mission against Vila.

This engagement was not considered major enough to be given a formal name by US Navy historians, but became known informally as the '1^st Battle of the Kula Gulf'.

The definitive 'Battle of the Kula Gulf' took place during the early stages of the US 'Toenails' campaign to take New Georgia, and occurred when a Japanese force landing reinforcements at Vila was intercepted by a force of US Navy cruisers and destroyers. One US light cruiser was sunk during the engagement while two Japanese destroyers were sunk and two more were damaged. The Japanese withdrew after the engagement, having landed 1,600 troops.

In the middle of 1943, in the wake of the 'Watchtower' campaign to take Guadalcanal island, the Allies launched their next offensive in the Solomon islands group, landing troops on the island of Rendova on 30 June as a preliminary step to seizing the major Japanese airstrip at Munda on New Georgia island. The US landing on Rendova established a forward beach-head from which to move troops across the Blanche Channel to New Georgia. After Rendova had been secured, the move to Zanana on the New Britain mainland took place on 2 July, after which US forces began a westward advance on Munda. In order to support this effort, and to prevent Japanese reinforcements from moving down the Munda trail from Bairoko, the Allies decided to land a force on the northern shore of New Georgia on 5 July. Meanwhile, the Japanese sought to reinforce the Munda area, moving troops and supplies via barge from the Shortland islands group via Kolombangara island.

On the night before the battle in the Kula Gulf, Rear Admiral Walden L. Ainsworth’s US Task Group 36.1 undertook a cruiser bombardment of Vila on Kolombangara island and also on Bairoko Harbour. This operation was undertaken to support a landing at Rice Anchorage on the northern coast of New Georgia by US Marine Corps and US Army troops tasked with capturing Enogai and Bairoko Harbour.

At the same time as the marines were landing at Rice Anchorage, two US destroyers, Strong and Chevalier, entered Bairoko Harbour to provide naval gunfire support. In the early hours of the morning a torpedo was spotted just before it impacted Strong on her port side aft, resulting in the loss of the destroyer. Some 241 survivors were rescued by Chevalier, while O’Bannon attempted to return fire. Some 46 US sailors lost their lives during the attack. The fatal Type 93 'Long Lance' heavyweight torpedo came from a salvo of 14 torpedoes fired by a group of four Japanese destroyers led by Niizuki. The torpedo travelled 12.5 miles (20 km), and this is believed to have been the longest successful torpedo attack of World War II. After firing their torpedoes, the Japanese destroyers departed the area without being detected. Such was the distance of the shot that the US commander believed that his force had been attacked by a Japanese submarine.

Ainsworth’s task group comprised the light cruisers Honolulu, St Louis and Helena, nd the destroyers Nicholas, O’Bannon, Radford and Jenkins. On the afternoon of 5 July, the task group was returning to the Coral Sea to resupply, when Admiral William F. Halsey, commander-in-chief of the South Pacific Area, was informed of another 'Tokyo Express' reinforcement and resupply mission down 'The Slot' in the Solomon islands group from Buin, on Bougainville island. Ordered to intercept the Japanese, Ainsworth changed course, and proceeded to the north-west past New Georgia island. Chevalier had been damaged while recovering survivors from Strong, and left the area; these two destroyers had been replaced by Radford and Jenkins, which departed Tulagi island, to the north of Guadalcanal island, at 16.47 and 18.37 on 5 July respectively, after replenishing.

The US ships passed Visu Visu Point, on the north-western coast of New Georgia island, just after 00.00 on 6 July. About one hour later, Ainsworth’s task group was off the eastern coast of Kolombangara island, about 880 yards (805 m) from Visu Visu Point, and roughly to the north-east of Waugh Rock, when it came into contact with a Japanese naval reinforcement group consisting of two transport units carrying troops, escorted by a support unit, under the command of Rear Admiral Teruo Akiyama. The Japanese force comprised 10 destroyers. The support unit comprised three ships of the 3^rd Destroyer Squadron, while the first transport unit (designated the 30^th Transport Division) comprised three destroyers, and the second transport unit (designated the 11^th Transport Division) comprised four destroyers. The Japanese ships were carrying 2,600 ground troops and were bound for Vila, which was being used as a staging point for the movement of reinforcements to Munda. When the battle began, Akiyama’s force was divided into two parts: the three escorts of the support unit (Niizuki, Suzukaze and Tanikaze) trailing the main column consisting of the four ships of the second transport unit (Amagiri, Hatsuyuki, Nagatsuki and Satsuki). Meanwhile, the three ships of the first transport unit (Mochizuki, Mikazuki and Hamakaze were unloading at Vila, about 8.5 miles (13.7 km) away.

The escorts of the Japanese support unit were the first to be engaged. Having tracked their opponents on radar, the US ships opened fire at 01.57, firing 612 shells in only very slightly more than 21 minutes, quickly sinking the destroyer Niizuki and killing Akiyama. However, Helena had expended all her flashless powder the previous night, and she was forced to use smokeless powder, thus illuminating herself to the Japanese ships with every salvo. Two of the Japanese destroyers launched 'Long Lance' torpedoes and hit Helena, fatally damaging her. After heading away from Vila following first contact, the main Japanese force broke away under cover of a smokescreen. In the process, Nagatsuki was hit by a single 6-in (152.4-mm) shell and ran aground near Bambari Harbour on Kolombangara, 5 miles (8 km) to the north of Vila, while Hatsuyuki was damaged slightly by two shells which failed to detonate.

At about 03.30, Ainsworth began retiring toward Tulagi island, while the Japanese headed for Buin. Two US destroyers, Radford and O’Bannon, remained behind to rescue survivors, as did the Japanese destroyer Amagiri. At about 05.00, Amagiri and Nicholas exchanged torpedoes and gunfire. Hit four times, Amagiri withdrew. The beached Nagatsuki was abandoned by her crew in the morning, and was later bombed and destroyed by US aircraft. Mikazuki and Hamakaze completed unloading, and departed through the Blackett Strait, while Mochizuki lingered for another hour before leaving through the Kula Gulf along the coast of Kolombangara island, in the process clashing briefly with Nicholas at about 06.15 before withdrawing behind a smokescreen.

The US losses during the battle were one light cruiser sunk and 168 men killed, all of whom were from Helena, while the Japanese lost two destroyers sunk and two destroyers damaged, with 324 men killed. The breakdown of casualties for the Japanese by ship was as follows: Niizuki 300 men killed, Amagiri 10 men killed, Nagatsuki eight men killed and 13 wounded, and Hatsuyuki six men killed. The Japanese succeeded in landing 1,600 troops at Vila, as well as 90 tons of supplies.

The destroyers Radford and Nicholas returned to rescue survivors from Helena. While recovering more than 750 men, Radford and Nicholas had to engage the Japanese three times. Amagiri escaped, and Hatsuyuki and Satsuki returned to Buin via the Blackett Strait.

Following the 'Battle of the Kula Gulf', the Japanese continued to move reinforcements south to New Georgia. On 9 July, 1,200 troops were moved to Kolombangara successfully and without encountering opposition. Another effort on 12/13 July, resulted in the 'Battle of Kolombangara', however. Meanwhile, on New Georgia, US troops had secured Enogai on the north-western coast on 10/11 July, while around Munda the Japanese stubbornly resisted US efforts to advance towards the airfield. The US effort stalled and was eventually halted by a Japanese counterattack on 17 July.