The submarine Enrico Toti returns to its base at the end of a mission. After a brief leave, the crew members, who have embraced their families, return to sea. They encounter a British submarine, HMS Triad, ram it, and sink it. The main character in the film was actually a submarine commander: Lieutenant Commander Bruno Zelich, who would die shortly after filming while commanding the submarine Sciré.
Practical Effects
Shot on actual Italian submarines with real sailors.
Direction
De Robertis invented naval docu-drama; no one else came close.

Director
Francesco De Robertis
Trivia, insights & behind the scenes
Lieutenant Commander Bruno Zelich died commanding the Sciré during the failed Raid on Alexandria in December 1941, before the film even premiered. He never saw his own performance.
De Robertis pioneered the 'film di guerra' style that influenced Rossellini's neorealism—this is where Italian cinema learned to find poetry in military procedure.