This was the Japanese occupation of the Gilbert islands group, a British protectorate in the Pacific (29 November/8 December 1941).
The Gilbert islands group comprises a chain of atolls some 2,500 miles (4025 km) to the south-west of the Hawaiian islands group and just to the north of the equator. The chain comprises hundreds of small islands with a total land area of just 166 sq miles (430 km˛). About 500 miles (805 km) long, the island chain is located about 300 miles (480 km) to the south-east of the Marshall islands group and just to the north-east of the Ellice islands group. The Gilbert islands were discovered by Europeans between 1764 and 1824 and named after a Royal Navy officer who visited in 1788, and in 1941 had only a small population of about 28,000 persons, primarily Micronesian with less than 100 Europeans. Most of the native population had adopted Christianity by 1941.
The islands were under British control in 1941 after being proclaimed a protectorate in 1892, ostensibly to protect the natives from exploitation by traders. The natives had a high degree of self-rule and British law prohibited land purchases by non-native persons. British oversight was exercised through a commissioner, on Ocean island, who also oversaw the Ellice, Phoenix, Fanning and other small island groups in the area.
There are 16 main atolls in the chain, none of which have elevations much greater than 12 ft (3.6 m), and consist of coral bedrock overlaid by sand and some poor soil sufficient to support some scrub and coconut palms. The island were relatively healthy for Westerners, with little incidence of malaria or other tropical diseases. The climate is uniformly warm and wet, with temperatures of 22° to 35° C (72° to 95° F) and annual rainfall averaging 150 to 180 in (3.80 to 4.0 m), but there are drought conditions every five to seven years.
The islands' infrastructure was limited to a lagoon-side road on each atoll and a few piers to accommodate ocean-going vessels. There were no airfields in the group prior to the arrival of the Japanese.
On 29 November 1941, in 'Gi' (i), Japanese troops of the 51st Guard Force departed Truk island in the Caroline islands group. This Gilbert Islands Invasion Force was carried in the minelayers Okinoshima and Tsuraru, coastal minelayer Tokiwa and transport Tenyo Maru, escorted by the destroyers Asanagi and Yunagi, and with the light carrier Chitose to provide air cover.
On 8 December the 51st Base Force occupied Makin island, where it set to work on the development of a seaplane base and radio station. The Japanese also make sporadic visits to nearby atolls in order to locate and net Allied coastwatchers and European civilians: the former were later killed, and the latter were interned. Following the US marine raider attack of 17 August 1942 on Makin island, the Japanese began to reinforce their garrisons and embarked on the fortification of Tarawa island, where they also built an airfield.