World War II

With the outbreak of World War II in the Asia–Pacific region, Japan began occupying New Guinea in 1942. As part of its war effort, the Japanese constructed a number of naval bases and military airfields across the region. On Biak Island, one such facility was built near the village of Ambroben, known as Mokmer Airfield. Constructed by the Japanese using rōmusha labor, the airfield featured a single coral-surfaced runway measuring 2,000 m by 40 m, with taxiways and revetments located to the north. Mokmer Airfield was successfully completed and became capable of supporting both single-engine and twin-engine military aircraft. Mokmer Airfield formed part of a larger complex of airfields on Biak Island—alongside Borokoe and Sorido—originally constructed by the Japanese. These airfields were considered highly strategic by the Japanese, as they supported the movement of troops, logistics, and other military operations against Allied forces in the Pacific Theater. The Allied forces also recognized the strategic importance of these airfields, as capturing the complex would enable them to launch attacks on Japanese positions in the Philippines, making it one of their primary objectives.

In anticipation of a possible landing on Biak, the airfield complex was heavily fortified by the Japanese. They devised an elaborate defensive strategy, allowing American forces to come ashore largely unopposed before advancing into a carefully prepared trap. This trap made use of a network of caves located west of Mokmer and east of Bosnek. The defensive system was designed to transform the area surrounding the vital airfields into a fortified network of caves and pillboxes, manned by riflemen and equipped with automatic weapons, artillery, and mortar batteries, as well as a company of Type 95 Ha-Go light tanks. The caves on the western side were interconnected by underground tunnels and were primarily constructed for combat purposes.

On 27 May 1944, Allied forces landed on Biak, marking the beginning of the Battle of Biak. The following day, they attempted to storm the airfield complex but were repulsed by heavy Japanese resistance and were eventually forced to withdraw. On 5 June, the 186th Infantry Regiment, with the 2nd Battalion of the 162nd Infantry Regiment attached, advanced to the eastern bases of the ridges overlooking Mokmer Strip. A coordinated assault was launched on 7 June, resulting in the capture of Mokmer Strip and the establishment of a beachhead to its south. However, Japanese resistance persisted—particularly from cave positions dominating the area—hindering efforts by engineers to improve the airfield. Engineering work resumed on 13 June but was again disrupted by Japanese counterattacks. Allied engineers were finally able to recommence sustained work on 20 June. Two days later, on 22 June, American forces broke through Japanese defenses and secured the coastal strip from Bosnek to Sorido, including the three airfields at Sorido, Borokoe, and Mokmer.

The Allies subsequently developed Biak into a major logistics base, constructing and rehabilitating several airfields across the area. On nearby Owi Island, U.S. engineers built multiple runways, while Mokmer Drome became operational by 22 June and was further improved and expanded with hardstandings for more than 100 aircraft through July and August. The airfields at Borokoe and Sorido were also redeveloped; however, work at Sorido was not completed due to limited manpower and unsuitable terrain. Although these airfields were not completed in time to support operations against the Marianas in June, they were later used in follow-on operations against the Palau Islands in September. Biak also served as a base for air strikes against targets in Mindanao and the Netherlands East Indies.

Major Allied units stationed on Biak Island

38th Bombardment Group (1–15 October 1944)

90th Bombardment Group (10 August 1944 – 26 January 1945)

345th Bombardment Group (July – 12 November 1944)

49th Fighter Group (5 June – 24 October 1944)

475th Fighter Group (14 July – 28 October 1944)

6th Reconnaissance Group (August – 3 November 1944)

71st Reconnaissance Group (8 August – 5 November 1944)

91st Reconnaissance Wing (10 August – 12 November 1944)

2d Combat Cargo Group (November 1944 – May 1945)

54th Troop Carrier Wing (5 October 1944 – 14 February 1945)

374th Troop Carrier Group (14 October 1944 – 28 May 1945)

375th Troop Carrier Group (14 October 1944 – 28 May 1945)

Dutch era

Postwar, the airfield complex became a major reclamation site for surplus Allied aircraft of various types. The Dutch administration soon took control of the facilities. Sorido Airfield was effectively abandoned following the end of the war and has since been converted into a naval base operated by the Indonesian Navy. Following the Proclamation of Indonesian Independence in 1945, commercial flights began operating to and from Biak using Borokoe Airfield, which had a 2,000 m runway. Mokmer Airfield was not in use at the time, and this remained the case until 1951.