The Woodlark Island group located in the Solomon Sea of the Pacific Ocean consists of Woodlark Island (now Muyua), Madau and Nusam Islands to the west, Nubara Island to the east, and the Marshall Bennett group to the southwest.
The main island, Woodlark Island (09°05' 45S, 152°41' 04E), is 36-miles (58-kilometers) long and from 5-to-17-miles (8-to-27-kilometers) wide for a total land area of 337-square-miles (873-square-kilometers). The island is generally a low, swampy raised coral platform covered with dense jungle but with a central core of Tertiary basement rocks exposed as a low, northerly trending range with some isolated hills in the central part of the island. Coral barrier reefs surround it except at Guasopa Bay (09°11' 58"S, 152°57' 13"E), the principal harbor accessible through two passages. Limited channel depth restricted the use of the harbor, but landing ships, tank (LSTs) could be brought to the beach for operations. Small supply ships anchored just offshore.
Woodlark had not been occupied by the Japanese and the U.S. Army, Navy and Marines landed on the island on 30 June 1943. The establishment of an airfield on the island was a necessary preliminary for (1) air operations against New Britain, Bismarck Archipelago and (2) the seizure of the Southeastern Bougainville Island, Solomon Islands to provide wider employment of air power and obtain closer support for operations. The construction of Guasopa Airfield (09°13' 38"S, 152°56' 49"E) was begun by the Seabees on 2 July and by 14 July the airfield consisted of single 3,000-by-150-foot (914-by-46-meter) runway which could accommodate Douglas C-47 Skytrains. By 21 July the runway was expanded to 5,200-feet (1,585-meter) runway with a coral surface. The first U.S. Army Air Forces (USAAF) fighter squadron arrived on 23 July with Bell P-39 Airacobras. The airfield was ultimately extended to 6,500-by-225-feet (1,982-by-69-meters)) with a parallel runway of 6,000-by-60-feet (1,829-by-18-meters) together with 110 hardstands. The airfield was also known as Woodlark Airfield and was used as a stopover point and refueling point. Defensive positions were set up around Woodlark with antiaircraft and coast artillery pieces installed, and machine gun and 37 mm beach positions established.
Naval Advance Base Woodlark Island was also built by the Seabees. A PT and landing craft repair base was also constructed at Guasopa Bay and the island was also used as a supply base. Road and housing construction and the establishment of a water system were begun by the Seabees. The first project after landing had been the cutting of trails into the coconut plantations and the surrounding jungle to allow immediate dispersal of all equipment and supplies. These trails were later developed into suitable roads, and by October, a 30-mile (48-kilometers) network of good hard roads had been completed. Housing was generally in floored and screened tents, although eight prefabricated wooden buildings and nine Quonset huts were provided for the USAAF, and a small hospital.
Three 3-by-7-foot (0.9-by-2.1-meter) pontoon barges were assembled and turned over to the naval base unit for operation. One 2-by-12-foot (0.6-by 3.7-meter) pontoon string was assembled and anchored offshore for use as a motor torpedo (PT) boat pier. The Seabees also did considerable repair work on landing craft, picket boats, and PT boats. Ample water supply was procured locally from several rivers. A sawmill, which was set up, provided 15,000-board-feet (35-cubic-meters) of lumber per day. A coral pit for road and airstrip surfacing material was also operated.
By 1 November 1943, all Seabees had been detached from Woodlark, except a maintenance unit which remained until March 1944.