'Fetlock' was the US occupation of Funafuti atoll in the Ellice islands group of the central Pacific (2 October 1942).

Comprising three reef islands and six true atolls, the Ellice islands group lies 2,600 miles (4185 km) to the south-west of the Hawaiian islands group and just to the south-east of the Gilbert islands group, which was occupied by the Japanese as an outer bastion for the defence of their bases in the Marshall islands group some 300 miles (480 km) to the north-east. The Ellice group’s atolls are disposed in a chain extending some 300 miles (480 km) from north-west to south-east, and in 1941 were under British control, the islands having become part of a colony with the Gilbert islands group in 1915 after being declared a protectorate in 1892, in order to protect the native population from exploitation by traders. The islanders were effectively self-ruling and British law prohibited land purchases by non-native persons. British oversight was exercised from Ocean island through a resident commissioner who also oversaw the Gilbert, Phoenix, Fanning and other small island groups in the area. In 1941 the island group’s population totalled 4,200 Polynesians and almost no Europeans. Some 2,000 residents had been voluntarily resettled in the previously uninhabited Phoenix islands group just before the outbreak of war in an attempt to reduce overpopulation.

The availability of bases in the Gilbert islands group opened the way for the Japanese to attack the southern flank of US task forces moving toward the Marshall islands group, and also provided advanced bases from which their aircraft could reconnoitre any Allied approaches in the southern arc.

Thus a US occupation of the Ellice islands group, some 700 miles (1125 km) to the south-east of the Gilbert islands group, would allow US aircraft to maintain and aerial surveillance over the Japanese bases being developed in the Gilbert islands group, and also to attack them.

The Japanese had occupied some of the Gilbert islands group in December 1941 and, after the US Marine Corps' raid on Butaritari during August 1942, also seized Nauru and Ocean islands in 'Ry' and began reinforcing Butaritari and Tarawa, a process that lasted into 1943. While the Japanese did not occupy any of the Ellice islands, they did bomb the administrative centre on Funafuti on several occasions after occupying the Gilbert islands group.

Three of the nine atolls comprising the Ellice islands group (Funafuti, Nanomea and Nukufetau) were occupied by US forces in October 1942 and August 1943 to secure the northern approaches to the Samoa and Fiji island groups on the primary Allied maritime route between the USA and Australasia, place the Japanese-held Gilbert islands group under surveillance, and support the forthcoming 'Galvanic' operation in the Gilbert islands group by providing bases for elements of the 4^th Marine Base Air Defense Wing and Major General Willis H. Hale’s 7^th AAF.

This preliminary to 'Galvanic' was undertaken by the Marine Corps' Defense Force, Samoan Group. In conjunction with the occupation of these islands, a US Army task force secured Baker island of the Phoenix islands in 'Turnover'.

Funafuti is a large atoll, some 13.5 miles (22 km) long and 10 miles (16 km) wide, located in the Ellice islands group to the south of the Gilbert islands group. The atoll has 30 islands, of which the largest is Fongafale in the north-east and which the Americans usually called Funafuti. This island is 8 miles (13 km) long and 50 to 150 yards (45 to 140 m) wide along most of its length widening to 700 yards (640 m) at one point. There are several passes navigable to shallow-draft ships, but the US Navy dredged Te Bua Bua Channel on the northern side to make it navigable to large ocean-going vessels. The population in 1941 was 680 persons.

The USA began construction of an airstrip on the wide section of Funafuti shortly before the war. However, the US Army refused a US Navy request to garrison the island early in 1942 to help protect the lines of communications to Australia.

'Fetlock' was undertaken 5^th Marine Defense Battalion, and the occupation was not revealed until after the Japanese discovered the fact on 27 March 1943. Ten Japanese air attacks were launched from Nauru island, staging through Tarawa island, between March and November 1943. On Funafuti atoll, 'Seabee' construction units built a 5,000-ft (1525-m) airfield on the main islet, and this facility was in service by the end of the month. By April 1943 this runway had been extended to 6,600 ft (2010 m), allowing it to be used by Consolidated B-24 Liberator four-engined heavy bombers for raids on Nauru on 20 April and Tarawa on 22 April. Small seaplane and PT-boat bases were also built.

As space ashore was very limited, the Service Squadron 4 floating naval base was activated at Funafuti, whose lagoon could accommodate as many as 100 ships, on 1 November 1943 to support operations into the Gilbert islands group, and a US Navy base ashore was commissioned on 15 November. All these improvements allowed forces based on or passing through Funafuti to support the 'Flintlock' and 'Catchpole' operations in the Marshall islands group.

It was at Funafuti that chartered tankers transferred their fuel to fleet oilers, which transported it into the combat zone to fuel warships.