The house flag of Mitsui Senpaku K. K., Tokyo. A white flag with a red motif. The flag is made of a wool and synthetic fibre bunting. It has a cotton hoist and is machine sewn. The design is printed. A rope and two Inglefield clips is attached.

Mitsui Senpaku KK was the original shipping department of the Japanese company Mitsui Bussan Kaisha, which was founded in 1876. The company ran steamships to transport coal. In 1904 the company moved to Kobe, Japan with a total of nine ships. By the end of World War I, the company owned 30 ships. In 1917, the company constructed a shipyard and began building its own boats. In 1920, it began running a service between Dalien, Kobe, and Seattle. The ships would operate as a liner service to Seattle, and on the return trips, they would pick up cargo at other ports. In the 1920s and 1930s, Mitsui expanded its operations to ports in New York, the Philippines, Bangkok, and the Persian Gulf. In 1937, the company owned 35 ships. In 1942, the shipping group of the company became independent and subsequently known as Mitsui Senpaku KK (Mitsui Steamship Company).

During World War II, all of Mitsui’s ships were under government control, and after the war the company’s fleet totalled only 17. The post-war period was a time of growth for the company, and between 1950 and 1964 the company built 35 ships. In 1964, the company merged with Osaka Shosen Kaisha to form the company Mitsui O.S.K., which is still operating today and is one of the most recognizable names in international shipping. The three bars on the flag appear to be a reference to the name Mitsui, which may be translated as ‘three wells’.