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Truk Lagoon, also known as Chuuk, is a sheltered body of water almost fifty miles long by thirty miles wide surrounded by a protective reef. Northeast of Australia, it is located mid-ocean at 7 degrees North latitude. The area consists of 11 major islands, and many smaller ones within the lagoon and is known today as the Chuuk islands, part of the Federated States of Micronesia in the Pacific Ocean. Its first colonial experience was as part of the Spanish Empire, then control was shifted to Germany after the Spanish-American War. It became a Japanese possession under a mandate from the League of Nations following Germany's defeat in World War I.

During World War II, Truk Lagoon served as the forward anchorage for the Japanese Imperial Fleet. The place was considered the most formidable of all Japanese strongholds in the Pacific. On the various islands, the Japanese Civil Engineering Department and Naval Construction Department had roads, trenches, bunkers and caves dug. Five airstrips, seaplane bases, a torpedo boat station, submarine repair shops, a communications center and a radar station were constructed during the war. Protecting these various facilities were coastal defense guns and mortar emplacements. At anchor in the lagoon were the Japanese Navy’s giant battleships, aircraft carriers, cruisers, destroyers, tankers, cargo ships, tugboats, gunboats, minesweepers, landing craft, and submarines.

Once the American forces captured the Marshall Islands, they used it as a base from which they launched an early morning attack on February 17, 1944 against the Japanese fleet in Truk Lagoon. Operation Hailstone lasted for three days with an American bombardment of the Japanese that resulted in the largest naval loss in history. Between then and the end of the War, more than 60 ships and 275 airplanes were sent to the bottom of the lagoon.

In 1969, the famous French oceanographer, Jacques Cousteau and his team explored Truk Lagoon. Following Cousteau’s 1971 television documentary about the lagoon and its ghostly remains, the place became a scuba diving paradise, drawing wreck diving enthusiasts from around the world to see its numerous and virtually intact sunken ships. Scattered mainly around the Dublon, Eten, Fefan and Uman islands within the Truk group, a number of the shipwrecks lie in crystal clear waters less than fifteen meters below the surface. In waters devoid of normal ocean currents, divers can easily swim across decks littered with gas masks and depth charges and below deck can be found numerous human remains. In the massive ship holds are row upon row of fighter aircraft, tanks, bulldozers, railroad cars, motorcycles, torpedoes, mines, bombs, boxes of munitions, radios, plus thousands of other weapons, spare parts, and other artifacts. Of special interest is the wreck of the submarine I-169 Shinohara which was lost when diving to avoid the bombing. The sub had been part of the attack on Pearl Harbor.

• Submarine I-169

Mitsubishi "Betty" bomber	Bow gun of the Fujikawa Maru	1930's truck in the hold of the Hoki Maru	2-man tank on the deck of the Nippo Maru
Light artillery piece on the deck of the Nippo Maru	Divers next to the mast of the Unkai Maru	Diver photographing 14-inch artillery shells in the Yamagiri Maru	Diver and soft corals next to the mast of the Hoki Maru