Hoki Maru
Chuuk
A Sunken Museum of Mechanized Warfare
The Hoki Maru stands as one of the most mechanically fascinating wrecks in the Pacific. While many ships in the lagoon carried ammunition or fuel, the Hoki Maru was a workhorse of the Japanese logistics chain, carrying the heavy equipment needed to build airfields and fortifications across the Mandated Islands. Today, those machines remain exactly where they were lashed down decades ago, now encrusted in a delicate layer of silt and sponge.
Descending onto the wreck, you are immediately struck by the contrast between the violent destruction of the midsection and the eerie preservation of the bow and stern. It is a site that demands multiple dives to truly appreciate; the sheer scale of the debris field and the complexity of the cargo holds offer a labyrinthine experience for those comfortable with overhead environments.
The Origins of the Hauraki
Long before she became a casualty of war, the vessel was known as the MV Hauraki, a handsome trans-Pacific freighter launched in 1922 for the Union Steam Ship Company of New Zealand. Built in Scotland, she was a pioneer of her era, powered by twin-screw diesel engines—a relatively modern feature for a merchant ship at the time. For nearly two decades, she was a familiar sight in ports from Vancouver to Sydney.
The ship’s civilian life came to a sudden end in July 1942. While en route from Fremantle to Colombo, the Hauraki was intercepted in the Indian Ocean by Japanese commerce raiders, the Aikoku Maru and Hokoku Maru. Rather than being sunk, the ship was captured, and her crew was taken prisoner, beginning a new and involuntary chapter under the Japanese flag.
Renamed the Hoki Maru, the vessel was pressed into service as a transport ship for the Imperial Japanese Navy. Her sturdy construction and large cargo holds made her an ideal asset for moving heavy equipment across the expanding Japanese perimeter. She spent the next two years dodging Allied submarines and supporting the far-flung garrisons of the Pacific.
Despite her Scottish roots, the Hoki Maru was quickly adapted to her new role. The Japanese crew painted over her original markings and installed defensive armaments, though her primary value remained her lifting capacity and internal volume. She became a vital link in the supply chain, often moving between Rabaul, Palau, and Chuuk.
The ship's history is a testament to the global nature of World War II. It is a rare thing to find a Scottish-built, New Zealand-owned vessel serving the Japanese Empire, only to be sunk by American carrier planes. This "identity crisis" is part of what makes the Hoki Maru such a unique subject for historians and divers alike.
By early 1944, the Hoki Maru found herself anchored in the "Gibraltar of the Pacific"—Chuuk (Truk) Lagoon. She was heavily laden with supplies intended for the defense of the region, unaware that the U.S. Navy was preparing to launch one of the most devastating carrier-based raids in naval history.
Operation Hailstone and the End in Chuuk
The Hoki Maru was positioned in the Fourth Fleet anchorage when Operation Hailstone commenced on February 17, 1944. Waves of American Dauntless dive bombers and Avenger torpedo bombers swarmed the lagoon, targeting the merchant fleet that sustained the Japanese base. The Hoki Maru was a priority target due to her size and the nature of her cargo.
During the initial strikes, the ship was hit by several bombs, but the fatal blow came from a torpedo that struck midship. The resulting explosion was catastrophic, likely sympathetic with the fuel or ammunition stored near the engine room. The blast was so powerful that it essentially folded the ship's midsection, causing it to sink rapidly in about 50 meters of water.
Today, the wreck lies on an even keel, but the destruction at its center is a sobering sight. The midsection is a chaotic jumble of girders and twisted plates, evidence of the immense heat and pressure of the explosion. Yet, the bow and stern remain remarkably intact, standing as silent sentinels over the devastation.
The Hoki Maru is most famous among divers for Hold Number 5. Inside, a fleet of Isuzu trucks, tractors, and even a primitive bulldozer sit in the darkness. The trucks are lined up in rows, their headlamps staring into the void and their wooden flatbeds long since rotted away, leaving only the chassis and engines behind.
Navigating the interior of the Hoki Maru requires careful buoyancy, as the silt is exceptionally fine. In the deeper sections of the hold, divers can find spare airplane propellers and radial engines. These components were destined for the nearby airfields on Eten or Param, but they never made it to the flight line.
The wreck serves as a permanent memorial to the hundreds of sailors and merchant mariners who lost their lives during the two-day raid. The Hoki Maru didn't just sink; she took a significant portion of the Japanese logistical capability with her, contributing to the eventual isolation and neutralization of Chuuk as a military stronghold.
The Underwater Truck Graveyard
The primary draw for most divers is the incredible collection of vehicles located in the aft holds. These aren't just rusted frames; you can clearly identify the grills, steering wheels, and even the rubber tires that have survived decades of immersion. It feels like a sunken construction site, frozen mid-task.
The presence of a steamroller and various tractors suggests the Hoki Maru was carrying an entire "airfield construction kit." Seeing these heavy machines—designed to build and create—sitting in the belly of a destroyed war machine provides a poignant contrast that few other wrecks can match.
The Torpedo "Fold"
The structural damage to the Hoki Maru is a fascinating study in naval architecture and explosive force. The midship section is so badly damaged that the ship appears to have been broken in two and then pushed back together. This creates a complex "canyon" of metal that divers can swim through.
While the damage is beautiful in its own way, it also serves as a warning. This area is the most unstable part of the wreck, with jagged edges and hanging debris. It provides a stark, physical reminder of the violence that occurred on that February morning, showing exactly where the torpedo's energy was vented through the hull.
Marine Life and Colonization
Because the Hoki Maru sits in a slightly more sheltered part of the lagoon, it has become a massive artificial reef. The upper decks are draped in soft corals and sea fans, while schools of jacks and occasional reef sharks patrol the perimeter. The contrast between the dark, industrial interior and the vibrant life on the exterior is stunning.
The wreck provides a perfect habitat for macro life as well. Nudibranchs and small crustaceans can often be found hiding in the rivets and rusted crevices of the winches. For photographers, the "balance" of the wreck—half war machine, half vibrant reef—offers endless opportunities to capture the resilience of nature.
"they stole my F@*#!* tractors"
Unknown Diver
On our April 2003 trip we heard a great story about these bulldozers. Apparently an ex-engineer from John Deere Tractor Corp was diving aboard the Thorfinn and was returning from a dive on the Hoki Maru. As the dive boat was nearing the Thorfinn there was a lot of commotion and yelling coming from the boat. The crew, thinking there had been an accident scrambled to get the first aid equipment ready. As the boat got closer they could make out what the guy was saying - "they stole my F@*#!* tractors".
Apparently, just prior to attack on Pearl Harbor, the MV Hauraki was carrying two of the world’s first hydraulic blade bulldozers. Partway into the journey, not long after Pearl Harbor’s attack, she broke down with first one and then two main engines failing. While standing still and with Japan now officially an Axis member at war, she was approached by the fully armed merchant cruisers 'Hokoku Maru' and ‘Aikoku Maru’. Afterwhich several shots were fired to gain a white flag of surrender. The MV Hauraki was commandeered by the Japanese, renamed the Hoki Maru, and the bulldozers were never seen again...until the day this engineer dived the Hoki Maru.
Other Must-Dive Wrecks of Chuuk Lagoon
Beyond the main highlights, Chuuk Lagoon offers a treasure trove of sites that are essential for any serious wreck diver. You can explore the lush soft corals of the Shinkoku Maru or see the massive 18-inch artillery shells still resting in the holds of the Yamagiri Maru. The Fujikawa Maru is famous for its "R2-D2" air compressor and accessible engine room, while the Amagisan Maru sits deeper, offering a haunting look at a large freighter and its resident tanker truck. For those interested in shallower depths, the Dai Ni Hino Maru provides excellent photographic opportunities with its bow gun, whereas the Hoki Maru remains a favorite for its cargo of well-preserved trucks and tractors. Finally, technical divers can push further to reach the iconic "Million Dollar Wreck," the San Francisco Maru, with its deck-mounted tanks, or pay their respects at the deep, somber remains of the Aikoku Maru.