'Capillary' was the US geographical rather than operational codename for Ocean island in the Pacific Ocean (26 August 1942/2 October 1945).

The island lies 240 miles (385 km) to the south-west of Tarawa atoll, 155 miles (250 km) to the south-east of Nauru island, its closest neighbour, and 420 miles (675 km) to the south-south-west of Jaluit atoll.

Ocean island is of oval shape, and is 1.75 miles (2.8 km) long on its east/west axis, about the same in width across its eastern end and 1.25 miles (2 km) wide across the central portion, and has an area of 2.3 sq miles (6 km²) inside its 6-mile (9.6-km) coastline. The island is a volcanic cone, the lip of the cone at a height of 266 ft (81 m) above sea level, where the caldera is shaped like a shallow dish. Ocean island’s coast is a narrow beach, and inside this is a gently sloped coastal fringe between 100 and 440 yards (90 and 405 m) wide. In 1941 much of the island was covered with brush and woodland, except where the strip mining of the island’s important phosphate deposits was under way. The mining had left limestone pinnacles up to 80 ft (24 m) tall, and the island is honeycombed with an extensive cave system, from which water was obtained as a result of rain­water seepage until the strip mining had made it possible for rain to be collected on the surface. The climate is similar to that of Nauru island. The south coast is slightly indented by Home Bay, flanked by Solomon’s Point on the island’s south-eastern corner and Lillian Point on the southern side. Near the point was Ooma, which was the European community. The bay offers little protection, but it was here that phosphate freighters were loaded. A road ran extended along the coastal fringe from the western end to a place near Solomon’s Point. Other roads ran into the cone to serve the mine.

Before the phosphate deposits had been discovered on Nauru in the first part of the 20^th century, no country had laid claim to Ocean island, but the UK immediately annexed the island on 28 November 1900, and the British Phosphate Company quickly began mining operations. The island was included in the Gilbert and Ellice Islands Crown Colony in 1916. The Micronesians of the Banaban native population retained ownership of the land and received royalties from the export of the phosphate, but did not work the mines.

At the beginning of the Pacific War, there were about 140 Europeans, 640 native Micronesians, 900 Chinese and 1,200 Gilbertese, and it was the indentured labourers of these two last groups who worked the mines.

On 9 December 1941 Japanese aircraft from a base in the Marshall islands group bombed Ocean island, thereby ending the mining operations. A troop of Australian artillery was then deployed to the island as its defence force, but both this most of the Europeans and Chinese were evacuated in February 1942 by a French destroyer and steamer. There remained six Europeans were the colonial adminis­trator, three New Zealand coastwatchers and two missionaries. In March 1941 Rabi island near Vanu Levu in Fiji, had been bought by the Australian government with Ocean islanders' phosphate royalty funds, and it was to this that the islanders were to be relocated, though this did not take place in time to escape subsequent events.

On 26 August 1942 the Japanese occupied Ocean island, and on this deployed a garrison comprising two companies of the 62^nd Guard Force from Jaluit atoll. It is believed that the six remaining Europeans were killed, but their remains were never found.

The loss of Nauru and Ocean islands caused a severe shortage of fertiliser in Australia and New Zealand, and the USA could provide only one-third of these countries' requirements. In August 1942 the Japanese reinforced their garrison on the island, and in February 1943 the defending unit was designated as the 62^nd Guard Force Dispatched Landing Force and placed under the command of the Gilberts Area Defence Force. The Japanese made no attempt to construct an airfield on Ocean island.

Most of the Banabans and Gilbertese were shipped away to Kusaie, Nauru and Tarawa as forced labourers, but about 160 Gilbertese were retained on Ocean island to fish and build fortifications for the Japanese: these men were to have been incorporated into the defence force had the island come under attack.

The Allies never planned to retake Ocean island, though they did fly frequent bombing raids.

Two days after the Japanese surrender on 15 August 1945, most of the remaining Gilbertese were murdered, though one man survived and was able to testify in the subse­quent war crimes trial.

On 2 October 1945 Lieutenant Commander Nahoomi Suzuki surrendered his garrison of 400 men to Brigadier J. R. Stevenson of the Australian army.

The phosphate deposits had been depleted by 1980 after all but 150 acres of the island’s 1,500 acres had been strip-mined, and the island was virtually abandoned. Some 4,000 Banabans now live on Rabi island, Fiji, to which they moved immediately after the war once collected from the various islands onto which the Japanese had deported them, and 300 remain on Ocean Island. The Gilbert, Line, and Phoenix Islands were granted independence by the UK in 1979 as the Republic of Kiribati, and Ocean Island was included in the new nation.