CONSTRUCTION AND EARLY SERVICE

In the bustling shipyards of Osaka, Japan, the Heian Maru began to take shape in the late 1920s. Commissioned by the Nippon Yusen Kaisha (NYK) shipping company, the vessel was one of three sister liners designed for stylish passenger travel and cargo transport across the North Pacific between Yokohama and Seattle. A flagship of speed and style, the Heian Maru was a fast and comfortable ship, reflecting Japan's burgeoning industrial capabilities and maritime aspirations. 

Design and Launch

Laid down on 20 February 1929 and launched on 24 April 1930, the Heian Maru was designed as a passenger-cargo liner, blending opulence with functionality. It was a symbol of Japan's maritime prowess and a testament to the skill and craftsmanship of its shipbuilders. The ship’s twin screw, eight cylinder propulsion system, powered by two steam turbines, enabled it to reach speeds of up to 18 knots, making it one of the fastest vessels of its kind.

The interior of the Heian Maru was equally impressive. It featured luxurious accommodations for passengers, including first-class suites, dining salons, lounges, and recreational areas, ensuring comfort and elegance during long voyages. The vessel also had ample cargo holds, capable of transporting significant quantities of goods, which made it an invaluable asset for NYK's commercial operations.

The Heian Maru embarked on its maiden voyage late in 1930, sailing from Kobe, Japan, to Seattle, Washington. The ship was a colossal presence on the seas and quickly gained a reputation for its reliability, speed, and luxurious amenities.

Early Service and Commercial Success

In its first 10 years of service, the Heian Maru played a crucial role in expanding NYK's reach and enhancing its reputation in the international maritime industry. The ship's regular trans-Pacific voyages were instrumental in facilitating trade and cultural exchange between Japan and the United States during a period of significant economic growth and modernization.

In addition to its passenger services, the Heian Maru was a vital cargo carrier. The ship's large holds could accommodate a wide variety of goods, including manufactured products, raw materials, and perishable items. This versatility, speed, and reliability made the Heian Maru an essential component of NYK's logistics network and were critical factors in its commercial success.

WARTIME SERVICE

As the 1930s progressed and global tensions escalated, the Heian Maru's role began to evolve. The ship's commercial success and strategic importance did not go unnoticed by the Japanese government. With the onset of World War II, the Heian Maru's luxurious passenger service would come to an end and she was the last Japanese ship to visit Seattle in August 1941 before war broke out several months later.

Requisition and Refit

In October 1941, the Imperial Japanese Navy requisitioned the Heian Maru with the aim of converting it into a submarine tender to support wartime operations. The ship’s luxurious fittings and promenade were stripped out to make way for the installation of repair facilities, storage spaces for torpedoes, fuel, provisions, and spare parts, and additional quarters to house submarine crews, providing a place to rest and recuperate between missions. To complete the refit, it was armed with four 6-inch guns and and two machine guns.

Equipped with workshops and specialized equipment, the Heian Maru’s primary role was to perform maintenance and repairs on submarines, and as such the ship traveled to various locations, providing logistical support, maintenance, and resupply services to submarines engaged in combat operations.

The Start of Wartime Service

Initially assigned to the Sixth Fleet, the Heian Maru’s first role was to rearm the infamous Japanese I-Boats operating in the waters around Hawaii. In February 1942, the ship had its first taste of battle near Kwajalein, Marshall Islands. US Naval planes from the USS Enterprise bombed and sank a number of Japanese vessels in the area, however, the Heian Maru escaped unscathed.

By the summer of 1942, Japanese operations in Hawaii had drawn to a close as the battle theater moved further west. Taking advantage of her impressive size and speed, the Heian Maru was reassigned to New Guinea and the Solomon Islands to transfer as many troops as quickly as possible to the region. The ship spent the remainder of 1942 running troops and supplies between Japan and Rabaul, PNG before experiencing her next brush with battle at Simpson Harbor, Rabaul on New Year’s Day 1943. However, despite two days of attacks from American B-17 and B-24 bombers, the massive ship remained at anchor in the harbor, amazingly unscathed.

With the Allied advance towards the Solomons Islands and New Guinea, the Heian Maru was moved to the relative safety of Truk Lagoon where it spent the first part of 1943. It was then deployed, along with the destroyer Fumitzuki, back to the Northern Pacific to assist with the evacuation of Japanese troops from the Aleutian Islands. During the summer of 1943, the Heian Maru returned to some of her former glory, serving as the headquarters for Rear Admiral Koda, the commander in chief of the evacuation operation. 

With ever-increasing tensions in the South Pacific, Japanese troops were desperately needed on the front line and the Heian Maru was the obvious choice to transport them. In September 1943, it joined a large convoy heading for Shanghai where 2,000 soldiers and a cargo of torpedoes embarked for the journey south. The convoy entered Truk Lagoon on 2 October 1943, torpedoes were offloaded, and the Heian Maru was underway again the following day, bows pointed towards Rabaul.

A Brief Reprise

After two years of wartime service, the Heian Maru was badly in need of an update to its meager weaponry. At the end of October 1943, it returned to Japan for several weeks of improvements which included fitting anti-aircraft machine guns and two huge 12-centimeter multipurpose guns. A sonar and depth charge rack were installed to manage the threat of submarine attack and an additional 242 crew were embarked to manage these new armaments.

The ship then returned to Truk Lagoon, and despite a brief encounter with the American submarine, USS Dace, arrived unscathed and anchored in the sheltered waters of the Sixth Fleet Anchorage. For the next few months, the Heian Maru returned to its original role as a submarine tender, supporting and re-arming the submarine fleet hunting American ships in the South Pacific. Its presence ensured that submarines could continue their missions without having to return to port for resupply or repairs.

Final Days

On 17 February 1944, Operation Hailstone commenced with a massive Allied air and sea attack on the Japanese fleet anchored in Truk Lagoon. That day, the Heian Maru was anchored next to its sister ship, the Hikawa Maru, which had been converted into a hospital ship for the war. The Heian Maru was also hosting Vice Admiral Takagi, and the staff of the Sixth Fleet. 

The ship’s crew and visitors could only watch on as the initial air battle raged overhead, but it wasn’t long before American Hellcat fighters turned their attention to the ships in the lagoon below. Despite numerous passes with their M2 .50 caliber guns blazing, the fighters inflicted minimal damage on the Heian Maru and finally returned to base. However, next to appear were the bombers, including a pair of SB2C Helldivers from the USS Bunker Hill. Setting their sights on the massive hulk of the Heian Maru, the bombers released their 1,000-pound bombs, hitting the water around the ship but, amazingly, missing a direct hit. One of the explosions was powerful enough to damage the No. 6 hold and the prop. shaft, and fires broke out around the ship’s stern. Overnight, the crew brought these fires under control and started to unload the cargo of torpedoes in a desperate attempt to mitigate severe damage from further attacks.

The Final Stand

The following day would be the final in the history of the Heian Maru. Unable to offload the entire cargo of torpedoes overnight, the exhausted crew of the ship were given no reprieve as a flight of SBD Dauntless bombers appeared over the lagoon at dawn on 18 February. With their targets firmly set on the Heian Maru, the bombers dropped their 1,000-pound bombs sending shockwaves through the ship’s superstructure. Two bombs rocketed into the midships area above the engine room and fierce fires erupted and spread quickly. For the next two hours, the crew fought to save the ship from the fires raging through the first class cabin area towards the bridge. 

It wasn’t long before another flight of bombers arrived with three of them focusing their efforts on the now severely hampered Heian Maru. More 1,000-pound bombs were released onto the bow of the ship but, miraculously, the remaining torpedoes in the forward No 1. hold did not detonate. By now, the entire ship was engulfed in flames, however, she remained afloat despite being under near-constant attack. With the realization that his ship was not going to survive the day, the captain ordered his crew to abandon ship and evacuate to the nearby submarine base on Dublon Island. 

The fatal blow came later in the day when TBF Avenger bombers swept over the lagoon to release their torpedoes on any ships still floating in the lagoon. Just after 2pm, the crew watched on as the huge hulk of the Heian Maru rolled to port and slipped to its final resting place on the bottom of Truk Lagoon.

EXPLORING THE WRECK

A testament to the quality of its build, the wreck of the Heian Maru is remarkably well-preserved, with much of its structure still intact. Resting on its port side in 135 feet of water, the sheer size of this ship requires several dives to explore it in full. One of the most striking features of the Heian Maru is the presence of numerous artifacts, including torpedoes, periscopes, and parts of submarine engines, which provide a tangible connection to its wartime role. The hull is encrusted with coral and marine life, creating a vibrant underwater ecosystem that contrasts with the silent steel remains.

Bow to Stern

Descending over the bow, the sheer size and scale of the Heian Maru makes it easily visible, even in the lowest light. The first striking feature of the wreck is the huge lettering in both Romanized and Kanji characters, stating the ship’s name in large bold letters ‘HEIAN MARU’.

Heading towards the stern on the outside of the wreck, the first hold is No.1 hold where the 53.3-centimeter torpedoes sit, still intact, after so many years. There are also a number of 12-centimeter shells stacked ready for use on the gun deck.

Continuing on towards the stern, divers reach the upper superstructure area which shows evidence of severe fire damage, and the companionway on the promenade deck where several submarine periscopes are lying around. The next area of interest is the bridge, however, not much remains here except for some broken stacks of china. Behind the bridge, the first area of bomb damage is evident, now a huge mass of twisted and damaged metal. Looking below, the outline of the funnel can be seen resting against the sand. 

The engine room is located midships and is absolutely massive with plenty of room for penetration. Squeezing in between the gangways, divers can easily spot the two huge diesel engines, still in the original fixings. Surprisingly, most of the pipework, valves, wheels, and gauges are all still in situ, surrounded by a maze of twisted metalwork.

Further towards the stern are more cargo holds and observant explorers might spot the intact medical kit. Finally, the ship’s name is once again visible above its two massive propellers. The upper-most propellor retained its hub while the lower one fell off. The rudder is also visible.

Marine Life

The wreck of the Heian Maru has become a thriving artificial reef, attracting a diverse array of marine life. Schools of tropical fish, including butterflyfish, angelfish, and barracuda, are commonly seen darting around the wreck. Macro enthusiasts will appreciate the abundance of nudibranchs, shrimp, and other small creatures that have made the ship their home.

Larger marine species, such as reef sharks and rays, are also frequent visitors to the wreck site. The combination of historical artifacts and abundant marine life makes diving the Heian Maru a multifaceted experience, appealing to both history buffs and marine biologists alike.

DIVE DEEPER

The Heian Maru is one of the most frequently requested wrecks on Dirty Dozen Expedition’s Truk lagoon itinerary. As one of the shallower wrecks in the lagoon, she is often dived early on in the trip with at least one further dive later on in the trip.

Liveaboard dives normally tie up to a midships mooring and we use a deco-bar for the 10 and 20-feet stops for added comfort. Runtime is usually around 120 minutes on CCR and 100 minutes on OC.

Find out more about joining a Dirty Dozen expedition and diving the Heian Maru, as well as the other spectacular wrecks of Truk Lagoon on our website or drop us an email at info@thedirtydozen.org.