In the late 1920s the Japanese shipping company Nippon Yūsen (NYK) began a major shipbuilding program, aimed at expanding its international passenger service.

[1] 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.

[6] Heian Maru, 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, who had received transit visas from Chiune Sugihara, Japanese consul in Lithuania.

[8] 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.

Throughout 1942 and into the early months of 1943, the Heian Maru shuttled between Japanese 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 the IJN 6th Fleet with torpedoes, provisions, spare parts, and replacement crewmen, but, with her capacious holds, was also used as a troop and general cargo transport.

Afterwards, she ferried torpedoes, distilled water, and other cargo to Truk, and, on 19 November, had a tense encounter with the American submarine USS Dace (SS-247) which tested her new commander, Captain Tamaki Toshiharu.

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.

Heian Maru quickly put to sea and went into evasive maneuvers north of Dublon Island - with Vice Admiral Takeo Takagi and his Sixth Fleet staff on board - but as one of the largest targets in the lagoon, enemy attacks were relentless.

The crew managed to correct the trim by pumping fuel to her bow tanks, and after sunset Heian Maru returned to Dublon, where Admiral Takagi and some of the ship's cargo of Type 95 torpedoes were offloaded.

Lying on its port side, some of the Heian Maru's cargo holds are 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.