Chuuk Lagoon

Descending into Chuuk Lagoon for the first time is like entering a museum that has been underwater for eighty years and has never been tidied up. The Fujikawa Maru lies on its port side at 30 meters, its gun turret still trained on the surface above, and the bow gun of the Shinyo Maru—a purpose-built Japanese aircraft carrier converted to an oil tanker—points at the sky as if still trying to make sense of the attack that sent it down. Schools of glassfish shoal in the engine room where the ceiling is thick with anemones, and a Napoleon wrasse the size of a sofa has taken permanent residence in the wheelhouse.

Operation Hailstone was a two-day raid by US Navy carrier aircraft on 17–18 February 1944 that destroyed most of the Japanese Combined Fleet's shipping in Chuuk. The raid sank twelve warships and thirty-two merchant vessels, killed roughly 2,500 Japanese personnel, and effectively ended Chuuk's use as a forward Japanese naval base. The human cost was enormous, and diving here requires an awareness that the wrecks are not just adventure scenery but war graves.

The lagoon itself is a natural fortress, a 80-kilometer ellipse of deep water surrounded by a coral ring wall that made it ideal for the Japanese naval headquarters. The visibility from the surface can exceed 30 meters on a calm day, and the walls of the outer reef drop vertically to well below sport-diving limits. Inside the lagoon, the wrecks are dispersed across a wide area, and live-aboard dive vessels are the practical way to visit more than a handful of sites in a single trip.

The Fujikawa Maru is widely considered the jewel of the lagoon, not because of its size—though at 136 meters it is one of the longest wrecks—but because of the completeness of its historical record and the way its cargo of aircraft parts, aviation fuel and military equipment remains visible in the holds. On a morning dive with good light, the propeller blades of the Zero fighters crated in hold number four catch the sunlight like mirrors.

Safety is the primary concern for all diving in Chuuk: the wrecks range from 15 to 60 meters depth, many have penetration passages that require advanced training to enter safely, and the US Navy Decompression Chamber is located on Weno island, the main population center, but may not be reachable within the golden hour for deep dives on the outer wrecks. Nitrox and proper gas management are strongly recommended for the deeper sites.

The local dive operators in Chuuk are experienced in managing these risks and most are accustomed to working with visitors who have significant wreck-diving certification. The standard of professionalism is high, but the responsibility for dive planning and personal limits rests with each individual diver, particularly on deep wrecks where nitrogen narcosis and decompression obligations are real constraints rather than theoretical ones.

Chuuk Lagoon holds the best-preserved collection of WWII shipwrecks in the world, with over 60 vessels accessible to recreational and technical divers.

The combination of deep and shallow wrecks, excellent visibility, and the natural protection of the lagoon makes it one of the few places where multiple major wrecks can be dived in a single trip without long boat rides.

The historical significance of Operation Hailstone gives the site a gravity that goes beyond the diving itself; it is one of the most important WWII maritime heritage sites in the Pacific.