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, with an area of 3130 km²  (considerably less according to other sources ). North of New Guinea, it is located mid-ocean at 7 degrees North latitude. The area consists of 11 major islands (corresponding to the 11 municipalities of Truk lagoon, which are Tol, Udot, Fala-Beguets, Romanum, and Eot of Faichuk group, and Moen, Fefan, Dublon, Uman, Param, and Tsis of Nomoneas group) and 46 smaller ones within the lagoon, plus 41 on the fringing coral reef, 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 built roads, trenches, bunkers and caves. 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. Some have described it as Japan's equivalent of the Americans' Pearl Harbor.
Downed airmen on an OS2U near Truk await rescue
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 Truk Lagoon. The Japanese withdrew most of their heavy units. Operation Hailstone lasted for three days, with an American bombardment of the Japanese wiping out almost anything of value - 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, 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 ships' 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.