This was the US geographical rather than operational codename, later changed to 'Fillet', for Jaluit atoll in the Marshall islands group of the central Pacific Ocean (1941/45).
Jaluit atoll is located near the southern end of the western Ralik group, and its nearest neighbour is Kili island some 30 miles (48 km) to the south-west. Kwajalein atoll is 245 miles (395 km) to the north-west and Majuro atoll about 110 miles (175 km) to the north-east. The atoll is similar to the others in the Marshall islands group in being approximately oval in shape and comprising reefs with numerous low islands and islets surrounding a lagoon. The islands are covered with palms, pandanus trees, and salt brush.
Jaluit is about 12 miles (19.25 km) across its broader southern end between East to West Points, but only 4 miles (6.4 km) wide at its northern end, and almost 30 miles (48 km) long on its west-north-west/east-south-east major axis. Of its 91 islands and islets, with a total land area of 4.38 sq miles (11.34 km˛), the largest is the long, narrow, L-shaped (with an extremely long vertical arm) Jaluit island. Along with the rest of the Marshall islands group, Jaluit was taken from the Germans in 1914 by the Japanese who, after World War I, received a League of Nations mandate over the Marshall islands group. Jabur island became the Japanese administrative centre of the Marshall islands group, and the Japanese developed a major naval base on Jaluit island, which possesses a deep and well-protected lagoon able to accommodate as many as 1,500 ships. A seaplane base able to operate four Mitsubishi F1M 'Pete' and two Aichi E13A 'Jake' floatplanes as well a 11 Kawanishi H6K 'Mavis' flying boats of the Yokohama Air Group, was built on Jaluit, but there was not the land area to permit the construction of an airfield. Other Japanese installations were on Emidj and Enybor islets to the north of Jaluit island, and the defence force was the 51st Guard Force.
Jaluit was the primary target of Rear Admiral Frank J. Fletcher’s Task Force 17 (centred on the fleet carrier Yorktown) during the US raid into the Marshall islands group on 1 February 1942. The aircraft of the Jaluit attack force met very bad weather and several aircraft failed to find any target, and the remainder inflicted only light damage on the 8,900-ton transport Kanto Maru.
By the time of the US invasion of the Marshall islands group late in 1944, the base’s fleet and air activities had been withdrawn, and after a US air mining effort on 4 January 1945 the Japanese closed the base.