History of Truk Lagoon
During the years following World War I when Japan was awarded a mandate over the islands of Micronesia, these islands were primarily looked upon as colonial territories that were ripe for exploitation and economic opportunity. The 1930s were marked by a hardening of Japanese nationalism and growing hostility towards Anglo-Saxon nations, primarily the United States. These islands were then recognized as a vital strategic area and plans were developed for their rapid militarization in the event of an impending war with the United States. Truk's status as a lesser settlement would change when naval planners began to look at the lagoon's strategic potential. Truk provided a huge lagoon that could serve as a natural harbor and several groups of high volcanic islands that could be effectively fortified. Entrances into the lagoon could be sealed off by placement of mines and the islands themselves could provide protective cover for the anchorages. With the development of flying boats and seaplane fighters, Truk's naval value was further enhanced because of the shallow water wind-protected areas surrounding the islands that provided ideal take-off/landing and anchorages for seaplanes. In addition, islands within the atoll could be cleared and leveled for airfields to accommodate land-based aircraft.
When attempts at extending the naval arms limitation system amongst leading naval powers broke down in the mid 1930s, the world's great powers were free to develop whatever naval strength they felt necessary to maintain their security. The elimination of the naval limitations system hurdle was the signal for the start of an unprecedented ship building program that would clear the way for Japan's development as a great maritime power. Japan's pledges to not fortify the islands of Micronesia were set aside and thus began the transformation of the islands for military purposes. Truk was changed into a forward area naval base that would become the most important naval base outside the Empire when it was chosen as the headquarters for the Japanese Combined Fleet. This fleet organization acted as the Japanese Navy's first line of defense or offense. Truk was to become the key staging point for sea and air operations between the Empire and its forward areas. Almost all major naval operations, including the attack against Pearl Harbour, were coordinated through Truk.
As a staging point and home to the Combined Fleet, a huge armada of ships was constantly scattered about the anchorages with more coming and going. Included were the super battleships Yamato and Musashi, lesser battleships, aircraft carriers, heavy and light cruisers, destroyers, patrol boats, picket boats, and fleet auxiliaries. Hundreds of land-based and floatplane aircraft could be found at any one time either stationed or in transit at the airfields and seaplane bases.
The two-pronged advance by the Allies on the Japanese home islands, one through the South western Pacific and the other through the Central Pacific, progressed to the point that Truk was a major roadblock. With Truk being located southwest of the Marshalls, east of Palau, and north of the Solomons- New Guinea area, it was obvious that if the naval base remained intact, the Combined Fleet could disrupt the Allied advances towards the Empire using its powerful warships, massive numbers of aircraft, and its re-supply capabilities to reach territories coming under attack. A photographic over flight over Truk by two Marine PB4Y Liberators on February 4, 1944, was a definite sign that the Combined Fleet was vulnerable and most of the major fleet units were moved out. Photos taken during the overflight showed large numbers of Japanese shipping within the lagoon. Because of its disposition, Truk appeared largely invulnerable to bombardment by surface ships. It appeared that only carrier-based air power could deal Truk a knockout blow. Up to this point, Truk had a mysterious reputation because little was known of it and there was a tendency by the Allies to overemphasize its strength.