The Koiari Raid (29 November 1943) was an unsuccessful attempt by the US Marines on Bougainville to interrupt a possible Japanese supply line to the south of the American beachhead on Empress Augusta Bay.
By late November the beachhead on Bougainville had been secured against the nearest Japanese troops, but General Griswold was worried that a major counterattack might come from the south, where the Japanese had strong forces. He decided to launch a raid against a Japanese base at Koirari, ten miles down the coast from Cape Torokina.
The raid was to be carried out by the 1st Marine Parachute Battalion (Major Richard Fagan), supported by a force from the 3rd Raider Battalion and a forward observer team from the 12th Marines. The Raiders provided 85 men and Fagan's battalion 529 men, for a total of 614 combat troops. The 1st Parachute Battalion was fresh, having only arrived on Bougainville on 23 November. The raid was to be supported some destroyers that were escorting a convoy to Bougainville.
The raid was originally timed for the morning of 28 November. On the night of 27 November a single boat checked the planned landing beach and reported that there were no Japanese troops present, but delays loading the parachute battalion onto their transport ships meant that the raid had to be postponed until the morning of 29 November. This meant that the paratroops wouldn't have the support of the destroyers, but some artillery support would be provided by a battery of 155mm howitzers posted at Cape Torokina.
The marine force was landed early in the morning on 29 November. The force was split, with the raider company and the HQ company 1,000 yards away from the main force. Much to the surprise of the main force instead of landing on an empty beach they found themselves right in the middle of a Japanese supply dump!
The marines quickly established a beachhead around 350 yards wide and 180 yards deep. The Japanese were equally surprised but soon organised themselves. The marines came under a rain of fire from 90mm mortars and grenades, and had to fight off a series of Japanese rush attacks. At about 9.30 the two missing companies joined the main force, having fought their way along the beach.
Fagan realised that his mission had failed, and sent a radio message to General Geiger asking to be evacuated. Geiger agreed to the request, but the return message never reached Fagan. During the day two attempts were made send landing craft to rescue the isolated raiders, but both were driven off by Japanese artillery. The 155mm howitzers were able to protect the Marine's left flank, but they were exposed to attack from the front and right. During the afternoon Fagan heard lorries coming from the south, and assumed that they were bringing reinforcements. He expected that the Japanese would launch a big attack on the following day, and wasn't optimistic about his force's chances.
Luckily the destroyers were still just about within range. General Geiger sent an urgent message asking for help, and just before 6pm the destroyers Fullam, Landsdowne and Lardner along with a LCI gunboat arrived off the coast at Koiari. The light was already fading, but the destroyers opened a radar guided bombardment. Between them the destroyers, the LCI and the 155m howitzers managed to produce a box barrage around the paratroopers. This allowed the landing craft to make a third and this time successful rescue attempt, and at 8.40pm the last Marines were withdrawn.
The failed raid cost the Marines 15 dead, 99 wounded and 7 wounded. Fagan estimated that the Japanese had lost 291 casualties, half wounded and half killed. The naval bombardment had caused a great deal of damage in the supply dump, but apart from that the raid had been a total failure.