Micronesia
A large atoll in Chuuk State, FSM, enclosed by a barrier reef and world-famous for the sunken WWII Japanese fleet from Operation Hailstone.
Chuuk Lagoon (formerly Truk Atoll/Truk Lagoon) is an atoll in Chuuk State, Federated States of Micronesia, about 1,800 km northeast of New Guinea. A protective barrier reef roughly 225 km around encloses a natural harbour some 79 by 50 km, with a total lagoon/harbour area of about 2,130 km2 and 93.07 km2 of land across 11 major and 46 smaller islands. Weno, in the lagoon, is Chuuk's state capital. The lagoon served as Japan's main Pacific fleet base in WWII and was devastated in the February 1944 US air raid Operation Hailstone, which sank dozens of ships and aircraft, making it one of the world's premier wreck-diving destinations. Source: Wikipedia (Chuuk Lagoon).