Chuuk Lagoon

Fifty ships and 275 aircraft, sunk in three days

Chuuk Lagoon, called Truk until 1990, is an atoll in the Federated States of Micronesia about 1,800 kilometres northeast of New Guinea. A reef 225 kilometres around encloses a natural harbour 79 by 50 kilometres, and Chuuk means mountain in the Chuukese language. People were living on Fefen and Weno by the 1st and 2nd centuries BC. Spain claimed the islands without ever settling them, sold them to Germany in 1899, and the Japanese Navy seized them in 1914.

In the Second World War the lagoon was the Empire of Japan's main naval base in the South Pacific. It was called the Gibraltar of the Pacific, though Japan had put its money into ships rather than fixed defences. Battleships, aircraft carriers, cruisers, tankers and cargo ships lay at anchor here, and Yamato and Musashi spent months in the lagoon around 1943. Warned by intelligence a week ahead, the Japanese moved their largest warships to Palau before American carrier aircraft struck on 17 February 1944. Operation Hailstone lasted three days. It sank 12 smaller warships and 32 merchant ships and destroyed 275 aircraft, most of them on the ground. British and Canadian forces attacked again in June 1945 in Operation Inmate, and the cut-off garrison ran short of food before the surrender.

The Truk Lagoon Underwater Fleet was added to the US National Register of Historic Places in 1976, and Chuuk is rated among the best wreck dives in the world. The Rio de Janeiro Maru is among the most visited wrecks, a 140-metre ship built in 1929 to carry Japanese emigrants to Brazil, later refitted as a submarine tender and sunk by a 1000lb bomb on the first day of the raid. She lies on her starboard side at up to 34 metres. In September 2025 divers saw oil leaking from her, the slick reached the shores of Panitiw, Nukanap and Sopota, and the governor of Chuuk declared a state of emergency and asked Japan and the United States for help. About 63 vessels are believed to lie in the lagoon, some of them at risk of leaking.