This movie is not an official sequel to The Bridge on the River Kwai (1957). It does supposedly follow-on from historical events as depicted in that film but the characters in both films are basically different.
The film's opening prologue states: "In February 1945, planes from the 493rd Squadron of the U.S. Army Air Corps bombed and destroyed the bridges on the River Kwai in Japanese-occupied Thailand. This film is based on the true events which happened during that period."
Brazil Maru was a 5,860-ton cargo ship, completed in 1919. Requisitioned by the Imperial Army (IJA) as a troop transport in October 1941. Just over 4 months after the events in this movie takes place, near the Inland Sea of Japan, the BRAZIL MARU strikes a mine about 1.5 miles off the Wada-misaki lighthouse and sinks near Kobe, Shikoku on May 25, 1945.