The Italian capitulation during World War 2 came on Sept. 8, 1943 and the Italian navy had been given orders to surrender their ships, but first they had to get out of Italy before the Germans captured them. The majority of the surface fleet sailed on Sept. 8 for the designated ports in North Africa and Malta, submarines at sea had to be contacted via radio and make to the port they were assigned to, they were also given instructions on what flag to fly and what recognition signals to make should they come under attack.

Topazio was one of the submarines at sea when the armistice was signed and she was ordered to Algeria, but she never arrived and to this day nobody knows what happened to her. The best evidence is that she was attacked and sunk by an RAF bomber on September 12, 1943 thirty or so miles southwest of Sardinia, but the bomber crew could not identify what boat they had attacked and since there were no survivors we can only assume that this attack caused the loss of Topazio. The submarine was supposed to be flying not only the Italian flag, but a black flag was to be flown from her periscope, the pilot of the attacking plane later stated that he saw no such flag. He also stated that he saw several crewmen abandon the boat, but none were ever found.