The Raid on Koiari was a battle that occurred between 28–29 November 1943 in the Pacific theater of World War II between American and Japanese forces. Part of the Bougainville campaign, the raid involved a landing by a battalion-sized force of United States Marines to harass Imperial Japanese Army troops on Bougainville Island. The raid was a failure for the Americans as they were attacked by a larger-than-expected Japanese force and as a result the Marines were withdrawn from the beachhead without having achieved any of their objectives.