The action off Horaniu (18 August 1943) was an unsuccessful American attempt to prevent the Japanese from establishing a barge base at Horaniu, on the northern coast of Vella Lavella.
The American invasion of Vella Lavella was one of the first examples of the leapfrogging strategy that would soon dominate the Pacific War. The Japanese had lost their base at Munda on New Georgia in the Solomon Islands, but they still had a large garrison on the next island to the west, Kolombangara. The Americans decided to leave the garrison of Kolombangara to wither on the vine and instead skip ahead to the next island in the chain, Vella Lavella. This was almost uninhabited, and the Japanese hadn't bother to occupy it.
The Americans landed at Barakoma, on the eastern side of the island, on 15 August. They found the island still undefended, although were the subject of a series of Japanese air strikes. The Japanese decided not to try and evict the Americans from Vella Lavella, but they did decide to establish a barge base at Horaniu, at the north-eastern corner of the island, to act as a staging post for a planned evacuation of Kolombangara.
The Japanese embarked two army companies and a platoon of naval troops on thirteen barges and three motor torpedo boats. They were directly supported by a covering force of light ships while four destroyers (Sazanami, Hamahaze, Shigure and Isokaze) under Rear Admiral Ijuin Matsuji provided a screen against any American interference.
The Americans responded by sending four destroyers under Captain Thomas J. Ryan (Nicholas, O'Bannon, Taylor and Chevalier) to intercept the landings. This force headed west along the Slot towards the seas north of Vella Lavella.
At about 11.30 on 17 August a force of Avengers found the Japanese and launched an unsuccessful attack on them. The flak from the Japanese ships did give away their position, so Ryan had some idea of the Japanese location a full hour before they appeared on his radar.
At 0.30am on 18 August 1943 the Japanese finally appeared on American radar, some 11 miles to their north-west. The barges were soon found a little further west. The Japanese destroyers were also moving west, on a similar course to the Americans.
At 0.50 Ryan ordered his ships to turn 30 degrees to the right, aiming straight at the barges. Three minutes later he altered course by another 30 degrees to avoid the barges (a move that also meant he evaded a salvo of torpedoes). He opened to repeat the successful torpedo attack carried out at Vella Gulf on 6 August, when a force of American destroyers sank three Japanese destroyers after torpedoing them from the side.
At 0.56 Ryan attempted to spring his trap by ordering his destroyers to turn 60 degrees to the left to head west towards the Japanese destroyers. At about the same time the Japanese opened fire, and then turned south, crossing the 'T' in front of the American column. If the Japanese gunfire had been accurate the Americans might have been in trouble, but the first salvo overshot by a quarter of a mile. At 0.58 Ryan turned eighty degrees to the right to head north, and the two fleets were back in parallel. The Americans also opened fire and at 1.00 they hit the Hamakaze, setting her on fire.
The gun battle only lasted until 1.03, when the Japanese began to pull out of range. The Chevalier had just fired her torpedoes, but the Japanese move meant that they sailed harmlessly by. The Americans zigzagged north until 1.11 when they turned north-west in an attempt to catch the Japanese. This exposed them to a torpedo salvo at very long range, but the Japanese also missed with all torpedoes. The Japanese destroyers were now faster than the Americans, and used their extra speed to make their escape.
In the meantime the barges carrying the troops escaped into the cover of the rugged coast of Vella Lavella. This just left the light covering forces, which now caught the full fury of the American destroyers. Two sub chasers, two motor torpedo boats and one armed barge were sunk and only one ship from the screen escaped. The Americans then retired from the area.
The troop transports were still intact, and on 19 August they landed their cargo at Horaniu. The barge base was up and running within a week, and remained in use until the advancing Allied forced its evacuation on 14 September. The Japanese retreated north-west along the coast of the island, until in early October the Japanese navy attempted to evacuate them, triggering the battle of Vella Lavella (6 October 1943).