The Raid on Koiari was a battle that occurred between 28 and 29 November 1943 in the Pacific theater of World War II between American and Japanese forces.

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for the Americans as they were attacked by a larger-than-expected Japanese force and as a result the Marines were withdrawn from the beachhead without having achieved any of their objectives.

The raiders were to harass enemy units as far inland as the East–West trail but avoid any decisive engagement with major Japanese forces.

The Marines overran the supply dump and hastily dug in 200 yards (180 m) inland, amidst heavy mortar, machine gun and rifle fire from defending Japanese.

[5] Realizing the futility of the situation and believing that he no longer possessed freedom of action having been decisively engaged, Fagan sent a request over the radio for evacuation.

[10] In December, US Army troops from Major General Oscar Griswold's XIV Corps had arrived to relieve the Marines around the perimeter.

[12] Following the defeat of the Japanese counterattack, a lull period followed until late 1944 when Australian forces arrived to relieve the American troops who were transferred to the Philippines.

The Australians subsequently undertook a series of advances across the island, which saw them clear the central sector and push north towards the Bonis Peninsula and south towards Buin.