page_title: Operation Hailstone
section_title: Background
hierarchical_section_title: Operation Hailstone / Background
context_page_description: Operation Hailstone, 17–18 February 1944, was a massive United States Navy air and surface attack on Truk Lagoon conducted as part of the American offensive drive against the Imperial Japanese Navy through the Central Pacific Ocean during World War II.
  Prior to Operation Hailstone, the IJN had used Truk as an anchorage for its large Combined Fleet. The coral atoll surrounding Truk's islands created a safe harbor where the few points of ingress and egress had been fortified by the Japanese with shore batteries, antiaircraft guns, and airfields.
  American estimates of Truk's defenses and its role as a stronghold of the Japanese Navy led newspapers and military men to call it the "Gibraltar of the Pacific", or to compare it with Pearl Harbor. Truk's location in the Caroline Islands also made it an excellent shipping hub for armaments and aircraft moving from Japan's home islands down through the South Seas Mandate and into the Japanese "Southern Resources Area".
  By early 1944, Truk was increasingly unsustainable as a forward base of operations for the Japanese.
context_section_description: 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 only began in earnest and in hurried fashion 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 (TGs) were committed to the operation. Their total strength consisted of five fleet carriers
  (the Enterprise,
  Yorktown,
  Essex,
  Intrepid, and
  Bunker Hill)
  and four light carriers (the
  Belleau Wood,
  Cabot,
  Monterey, and
  Cowpens), carrying a total of 500+ warplanes. 
  Supporting these aircraft carriers was a task force of seven battleships, and numerous heavy cruisers, light cruisers, 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 Japanese sightings of U.S. Marine Corps PB4Y-1 Liberator reconnaissance planes sent to reconnoiter the area.
caption: Map of the Caroline Islands