the war, cut off and surrounded by the American island-hopping campaign in the Central Pacific, which also bypassed important Japanese garrisons and airfields in the Bismarck Archipelago, the Caroline Islands, the Marshalls, and the Palaus. Meanwhile, the Americans built new bases from scratch at places including the Admiralty Islands, Majuro, and Ulithi Atoll, and took over the major port at Guam. Background The Japanese occupied Micronesia, including the Caroline Islands, in 1914, and established Truk as a base as early as 1939. The lagoon was first built up to house the IJN's 4th Fleet, its "South Seas Force". After the outbreak of war with the United States, the 4th Fleet was put under the command of the Combined Fleet, which continued to use Truk as a forward operating base into 1944. In addition to anchorages for warships, and port facilities for shipping between the home islands and the Southern Resources Area, five airfields and a seaplane base were constructed at Truk, making it the only major Japanese airfield within flying range of the Marshall Islands. Despite the impressions of U.S. Navy leaders and the American public concerning Truk's projected fortifications, the base was never significantly reinforced or protected against land attack. In fact, the development of Truk began in earnest, and in hurried fashion, only in late 1943, when the airfields were extended, shore batteries were erected, and other defensive measures taken against a U.S. invasion. Because aircraft stationed at Truk could potentially interfere with the upcoming invasion of Eniwetok, and because Truk had recently served as a ferry point for the resupply of aircraft to Rabaul, Admiral Raymond Spruance ordered Vice Admiral Marc A. Mitscher's Fast Carrier Task Force, designated TF 58, to carry out air raids against Truk. Three of TF 58's four carrier task groups were committed to the operation. Their total strength consisted of five fleet carriers (the , , , , and ) and four light carriers (the , , , and ), carrying a total of 500+ warplanes. Supporting these aircraft carriers was a task force of seven battleships, and numerous heavy cruisers, light cruisers, 28 destroyers, and submarines. The Japanese, meanwhile, understood the weakness of their position at Truk. The IJN had begun withdrawing fleet units from its anchorages as early as October 1943. The effective abandonment of Truk as a forward operating base accelerated during the first week of February 1944, following