Just one month after landing on Hollandia, American and Australian forces landed on Biak Island, Dutch New Guinea. This operation developed into a particularly bloody campaign, as Japanese defenders took refuge in the caves that honeycombed the island and fought bitterly and tenaciously, often to the death. Allied troops faced particularly difficult conditions in terms of food shortages, illness, and foul wet weather.

We have landed on Biak Island. . . . The capture of this stronghold will give us command domination of Dutch New Guinea except for isolated enemy positions. For strategic purposes this marks the practical end of the New Guinea campaign. The final stage has also been reached in the offensive initiated in this theater on 29 June 1943, by the combined forces of the Southwest Pacific and the South Pacific Areas. It has resulted in the reconquest or neutralization of the Solomons, the Bismarcks, the Admiralties, and New Guinea. From the forward point reached by the Japanese we have advanced our front approximately 1,800 statute miles westward and approximately 700 miles to the north. . . . Compared with the enemy our offensive employed only modest forces and through the maximum use of maneuver and surprise has incurred only light losses. The operations have effected a strategic penetration of the conquered empire Japan was attempting to consolidate in the Southwestern Pacific and have secured bases of departure for the advance to its vital areas in the Philippines and the Netherlands East Indies.

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Further Reading
Charles A. Willoughby et al., eds., Reports of General MacArthur: The Campaigns of MacArthur in the Pacific, 2 vols. (Washington, DC: U.S. Government Printing Office, 1966), 1: 118–120. .