Chuuk Lagoon was the Empire of Japan's main naval base in the South Pacific theatre during World War II.

The area consists of eleven major islands (corresponding to the eleven municipalities of Truk lagoon, which are Tol, Udot, Fala-Beguets, Romanum, and Eot of Faichuk group, and Weno, Fefen, 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.

[6] The first recorded sighting by Europeans was made by Spanish navigator Álvaro de Saavedra on board the ship Florida during August or September 1528.

The Spaniards stopped to raise a flag over Chuuk in 1886 and returned in 1895 as part of an attempt to assert control and negotiate peace between warring Chuukese tribes.

During the First World War, the Japanese Navy was tasked with pursuing and destroying the German East Asia Squadron[10] and protection of the shipping lanes for Allied commerce in the Pacific and Indian Oceans.

[11] During the course of this operation, the Japanese Navy seized the German possessions in the Marianas, Carolines, Marshall Islands and Palau groups by October 1914.

At anchor in the lagoon were battleships, aircraft carriers, cruisers, destroyers, tankers, cargo ships, tugboats, gunboats, minesweepers, landing craft, and submarines.

Forewarned by intelligence a week before the U.S. raid, the Japanese had withdrawn their larger warships (heavy cruisers and aircraft carriers) to Palau.

Once the American forces captured the Marshall Islands, they used them as a base from which to launch an early morning attack on 17 February 1944 against Truk Lagoon.

The Japanese garrison on Eniwetok was denied any realistic hope of reinforcement and support during the invasion that began on 18 February, greatly assisting U.S. forces in their conquest of that island.

Truk was isolated by Allied forces, as they continued their advance towards Japan by invading other Pacific islands, such as Guam, Saipan, Palau, and Iwo Jima.

Cut off, the Japanese forces on Truk and other central Pacific islands ran low on food and faced starvation before Japan surrendered in August 1945.

Scattered mainly around the Dublon (Tonowas), Eten, Fefan and Uman islands within the Truk group, several shipwrecks lie in crystal clear waters less than fifteen metres (50 ft) below the surface.

In the massive ships' holds are the remnants 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.

[25] On 12 April 2011, the Australian Broadcasting Corporation program Foreign Correspondent screened a report on Chuuk Lagoon likening the effect of the impending massive release of tens of thousands of tonnes of oil from the rusting Japanese warships into the coral reef to that of the Exxon Valdez spill in Alaska.