When the Japanese acquired the Caroline Islands from Germany as a League of Nations mandate after World War I, they found themselves in possession of Truk (present-day Chuuk), an atoll studded with islands that enclosed a natural deep-water harbor spanning 820 square miles. During World War II this “Gibraltar of the Pacific” was a key staging base for imperial ships and aircraft. Thus when the U.S. Navy invaded the Marshall Islands in late January 1944, Truk came under the sights of the Fast Carrier Task Force under Adm. Marc A. “Pete” Mitscher.

Launched that February 16, Operation Hailstone devastated the many Japanese bases on Truk, destroying or crippling more than 250 aircraft and sinking 32 transport ships, two light cruisers, four destroyers and four auxiliary vessels. The American attackers lost just 25 aircraft and 40 crewmen. By the time the American fleet departed on February 18, the bogey of the Japanese Gibraltar had been laid to rest. Follow-up carrier raids in late April finished its importance as a Central Pacific base. What remains is a seabed littered with the rusting and coral-encrusted remains of aircraft, ships and their cargoes, reminders for recreational scuba divers of the ferocious battle that once raged there.

  • An American torpedo starts the Japanese freighter Amagisan Maru on her voyage to the bottom. At right: Cargo items and human remains mark the resting place of the freighter Kiyosumi Maru. (Naval History and Heritage Command)
  • A diver lights up a coral-encrusted Type 97 Ha-Go light tank sunk aboard the freighter San Francisco Maru. (Waterframe, Alamy)
  • The ship’s wheel and engine-order telegraph highlight the bridge of the freighter Nippo Maru. (Waterframe, Alamy)
  • The Japanese used this Mitsubishi G4M2 Betsy bomber to reconnoiter the U.S. Fifth Fleet until downed by a Grumman F6F-3 Hellcat in Truk Lagoon. (Amanda Cotton, Alamy)
  • A diver swims over San Francisco Maru’s open cargo hold. (Chris A. Crumley, Alamy)
  • This remarkably intact G4M2 likely ditched after being crippled by the Fast Carrier Task Force’s air patrol. (Horizon Images/Motion, Alamy)
  • Divers pass a Type 97 light tank while exploring San Francisco Maru. (Chris A. Crumley, Alamy)
  • A Nakajima B6N1 Tenzan torpedo bomber that failed to strike the U.S. task force adds its wreckage to Truk Lagoon’s carpet of war junk. (Rob Atherton, Alamy)
  • Its engines forever stilled, a Kawanishi H8K2 flying boat supports new life on the floor of the lagoon. (Pacific Press, Alamy)