Heian Maru (平安丸) was a Japanese ocean liner launched in 1930 and operated primarily on the NYK line's trans-Pacific service between Yokohama and Seattle. Shortly before the outbreak of the Pacific War, it was requisitioned by the Imperial Japanese Navy and converted to use as an auxiliary submarine tender. In 1944 it was sunk by American aircraft at Chuuk Lagoon during Operation Hailstorm. Its submerged hulk – the largest of Chuuk's "Ghost Fleet" – remains a popular scuba diving destination.