Heian Maru (1930)

The Heian Maru was a Japanese ocean liner launched in 1930 and operated primarily on the NYK line's Yokohama-Seattle route. Shortly before the outbreak of the Pacific War, it was requisitioned by the Imperial Japanese Navy and converted to use as a submarine tender. In 1944 it was sunk by American aircraft at Chuuk Lagoon, where its submerged hulk – the largest of Chuuk's "Ghost Fleet" – remains a popular diving destination.

Background
In the late 1920s the Japanese shipping company Nippon Yūsen (NYK) began a major shipbuilding program, aimed at expanding its international passenger service. Of eight passenger liners built, three were of the Hikawa Maru class, designed mainly for service on NYK's Yokohama-Seattle route. The three ships were the Hikawa Maru, Hiye Maru, and Heian Maru.

Construction of the Heian Maru, planned as an 11,616-ton combined passenger-cargo liner, began 19 June 1929 at Osaka Iron Works. It was named in honor of Kyoto's historic Heian Shrine and launched on 24 November 1930. Fitting out was completed on 24 November, and on 18 December Heian Maru began her maiden ocean crossing, from Hong Kong to Seattle.

Ocean liner
The Heian Maru entered regular service, delivering passengers, cargo, and mail, her initial route being Hong Kong, Shanghai, Moji, Kobe, Yokohama, Victoria and Seattle, with occasional stops at Yokkaichi, Nagoya, and Shimizu.

From early 1935 she ran on the Osaka to Seattle route, with calls at Kobe, Nagoya, and Shimizu. The return trip was to Yokohama, Kobe and Osaka. From April 1935 most voyages started and finished at Kobe, with stops at Yokohama, Vancouver, and Seattle. Due to the speed of Heian Maru and her two sister ships, NYK was able to maintain regular departures from Seattle for Yokohama every three weeks.

The Heian was a fast, modern, mid-sized liner capable of taking 300 passengers across the Pacific in comfort. Her interiors were done in Old English style, and when opened for tours in Seattle she attracted thousands of visitors. One 1934 American passenger described the galley's attempts as American-style food as poor, but was impressed by the vessel's compactness of design, clever engineering, and professional crew.

On 26 July 1941, President Roosevelt ordered the freezing of all Japanese assets in the U.S. The Heian, en route to Seattle, was forced to spend two days sitting 150 miles off Cape Flattery while officials worked out a guarantee that the ship would not be seized once it entered American waters. Among the passengers, waiting anxiously, were numerous Jewish refugees from war-torn Europe. Once in port the ship refused to discharge its cargo of raw silk (valued at $1,000,000) bound for New Jersey mills. After being served with papers for five separate legal claims, the ship's crew agreed to offload the cargo. All passengers disembarked in Seattle, including 69 bound for Vancouver, B.C. Further diplomatic furor arose when, among 144 Japanese passengers preparing to board the ship for the return voyage to Yokohama, both men and women were stripped to their underwear and searched by American officials. The ship sailed from Seattle for the last time on 4 August 1941.

Submarine tender
As the Heian Maru returned to Japan in August 1941, NYK was informed that due to rising tension between Japan and the U.S., the liner would be converted to military use. On 3 October the ship was formally requisitioned by the Imperial Japanese Navy, as a submarine tender with the Yokosuka Naval District. Two weeks later conversion was begun at Mitsubishi Heavy Industries in Kobe. Amongst numerous other alterations, four 150mm cannon, two dual-mount machine guns, two searchlights, and a rangefinder were installed.

The outbreak of World War II in the Pacific on 7 December 1941 (8 Dec. in Japan) found Heian still being refitted, but by the end of the month she was on her way to Kwajalein to take up a new posting with Sixth Fleet (Submarines), SubRon 1, Combined Fleet. In early February 1942, while at Kwajalein, Heian's crew got their first taste of combat during raids launched from the American aircraft carrier USS Enterprise (CV-6).

Throughout 1942 and into the early months of 1943, the Heian Maru shuttled between IJN bases at Truk (later known as Chuuk) atoll, Rabaul in the Solomon Islands, and Yokosuka and Kure, in Japan. She performed her designated task of supplying the dozen submarines of SubRon 1 with torpedoes, provisions, spare parts, and replacement crewmen, but, with her capacious holds, was also used as a troop and general cargo transport. At Rabaul in January 1943 Heian was caught in two major Allied aerial attacks, during which she narrowly avoided bomb hits. On 2 June 1943 the Heian Maru arrived at Paramushiro in the Kuril Islands to support operations in the Aleutian Islands. She was used as a floating command post for the secret, successful withdrawal of 5,000 Japanese troops from the island of Kiska, then returned to Yokosuka on 14 August.

Over the next several months, Heian was busy transporting troops, vehicles, and other supplies from Shanghai to Truk and Rabaul. After a brief refit in Japan she ferried torpedoes, distilled water, and other cargo to Truk, and, on 19 November, had a tense encounter with the American submarine USS Dace which tested her new commander, Captain Tamaki Toshiharu. She spent December 1943 and January 1944 disbursing supplies to submarines and other ships of the Combined Fleet at Truk lagoon.

The Japanese naval base at Truk was a large, sprawling complex, with hundreds of vessels anchored among dozens of islands, surrounded by a protective reef. The islands were studded with airfields, hospitals, repair shops, storage sheds, fuel depots, command facilities, and the villages of Pacific Islanders who were used as forced labor. It was defended by coastal guns in concrete casements, hundreds of fighter planes, and thousands of anti-aircraft guns of all types, both on ship and shore. The Heian Maru was moored next to her sister ship the Hikawa Maru (in wartime service as a hospital ship) on the leeward side of Dublon Island when, on the morning of 17 February 1944, the Americans launched Operation Hailstone.

Carried out by the US Navy's Task Force 58, with nine aircraft carriers, under the command of Vice Admiral Marc A. Mitscher, Hailstone was a massive, two-day combined air-surface-submarine raid. Although the IJN had moved its aircraft carriers and battleships from Truk a short time earlier, their defenses were unprepared for the scale of the attack, and the remaining navy and merchant vessels were devastated as wave after wave of American warplanes came roaring in. The Heian Maru quickly put to sea and went into evasive maneuvers north of Dublon Island - with Vice Admiral Takagi and his Sixth Fleet staff on board - but as one of the largest targets in the lagoon, enemy attacks were relentless. At mid-morning two bombs fell close astern, damaging one of her propeller shafts and flooding an aft hold. The crew managed to correct the trim by pumping fuel to her bow tanks, and after sunset Heian returned to Dublon, where Admiral Takagi and some of the ship's cargo of Type 95 torpedoes were offloaded.

Early the following morning, 18 February 1944, the Heian Maru got underway as the American aerial attacks resumed. Shortly after 3am she was struck, in quick succession, by two pairs of bombs; fire engulfed the bridge and threatened the hold containing the remaining torpedoes. The wounded ship began sinking, and at about 5 am Captain Tamaki gave the order to abandon ship. Most of the crew, including Tamaki, reached the shore safely, but a total of 18 men were killed, and 25 wounded.

At 9.30 am, Grumman TBF Avenger torpedo bombers from USS Bunker Hill attacked the still-burning Heian Maru, a torpedo striking her amidships on the port side. She sank soon after, resting on her port side in about 110 feet of water.

On 31 March 1944 the Heian Maru was removed from the Navy List.

Dive site
Chuuk Lagoon, in the Caroline Islands, now part of the Federated States of Micronesia, is a popular destination for recreational/sport divers around the world. In the 1960s, scuba divers began locating and identifying the hulks of Japanese ships sunk during Operation Hailstone (as well as later raids). The lagoon became well known as the subject of a 1971 episode of The Undersea World of Jacques Cousteau, titled 'Lagoon of Lost Ships'. Of the roughly 45 ship wrecks that make up Chuuk's "Ghost Fleet", the Heian Maru is among the most popular with divers. Its depth of about 33 meters (12 meters on upper/starboard side), in relatively clear, still waters, makes it accessible to moderately experienced scuba divers. It is the largest wreck in the lagoon (the somewhat larger Tonan Maru no. 3 was refloated post-war), and its name is still clearly visible on the bow, in both English and Japanese. Lying on its port side, some of the Heian's cargo holds are fairly accessible, revealing stockpiles of torpedoes, artillery shells, submarine periscopes, and numerous other items.

In recent years there has been growing concern by Chuukese and environmental groups over potential damage to the lagoon as the slowly corroding wrecks begin leaking heavy fuel oil.

The Heian Maru and other Japanese wrecks in Chuuk Lagoon are officially designated as war graves by the Japanese government.