The Montevideo Maru was a Japanese auxiliary vessel. Prior to the Second World War, it operated as a passenger and cargo vessel, travelling mainly between Asia and South America.

On June 22nd, 1942, some weeks after the fall of Rabaul, the Montevideo Maru was on that city, where nearly eleven hundred war prisoners, mainly Australians, where embarked.

She proceeded without any escort to the Chinese island of Hainan, when the ship was sighted by the American submarine Sturgeon near the northern Phillipinean coast, on June 30th. The Sturgeon then fired two torpedoes at the Montevideo Maru, which sank on the dawn of July 1st.

Source:

http://www.jje.info/lostlives/exhib/potp/montevideomaru.html