In his 2008 autobiography "My Word Is My Bond", Sir Roger Moore recalled that Lee Marvin got into a fight with Japanese journalists at an airport while making this movie. He said Marvin still hated the Japanese because of his war experiences.
Sir Roger Moore and Lee Marvin got into a fight during filming, which Moore won. Marvin recalled, "The guy is built like granite. Nobody will ever underestimate him again."
The story of this movie was inspired by one of the most spectacular and adventurous events that took place during World War I, in German East Africa, later Tanganyika, later Tanzania, in late 1914 to July 1915, known as the Battle of Rufiji Delta, in which the German light cruiser S.M.S. Königsberg was blockaded, and finally damaged by British forces. Two units were shallow-draft vessels known as "monitors" that were built for the Brazilian Navy but taken over by the Royal Navy shortly before the start of WWI. When it became clear that larger ships couldn't successfully enter delta to sink the ship. The Royal Navy sent in the monitors which inflicted damage on Königsberg. The Germans scuttled and stripped the ship of all ten 4.1 inch guns. Mounted on improvised gun carriages, these guns were used to great effect by German-led guerilla forces commanded General Paul von Lettow Vorbeck.
Lee Marvin was less than four years older than Sir Roger Moore.