Truk Lagoon holds the largest concentration of shipwrecks on Earth — an entire Japanese fleet sunk in a single 48-hour attack. Through World War II this vast atoll in the Federated States of Micronesia was the Imperial Japanese Navy's main Pacific stronghold, so heavily fortified it earned the nickname Gibraltar of the Pacific, its 225-kilometre reef enclosing a natural harbour nearly 80 kilometres across. In February 1944, American carrier aircraft caught the fleet at anchor during Operation Hailstone and, in two days, sent more than forty ships and some 250 aircraft to the bottom — the heaviest loss of shipping Japan suffered in the entire war. Freighters, tankers, submarine tenders and warplanes settled onto the lagoon floor, and there most of them still lie.
Eight decades of coral growth have turned that sunken fleet into the world's greatest wreck-diving site. On the Fujikawa Maru, a freighter resting upright in about 34 metres of water, soft coral sheathes the deck gun while a forward hold still cradles the fuselages of nine dismantled fighter planes; nearby wrecks hold gas masks, sake bottles and even light tanks, sitting where they came to rest in 1944. Sunlight filters through warm, current-free water onto hulls that have barely shifted, now draped in coral and circled by reef fish. These are protected war graves that still hold the remains of hundreds of sailors; French oceanographer Jacques Cousteau's 1969 expedition first drew the world's divers here. Above the surface the lagoon stays placid and warm, ringed by palm-covered volcanic islands where village life goes on much as it always has.