September 15, 1942 the Italian submarine Smeraldo departed Augusta, Sicily to patrol off the coast of Tunisia, she was never heard from again. She was built in Taranto in 1933 and conducted several war patrols, but never sank a single ship. The boat has not been found to this day, perhaps she hit a mine or suffered some catastrophic mechanical failure like a hull breach. She had been the victim of a vicious depth charge attack in which over 200 charges were dropped on her in July of 1941. However there is no evidence that the repairs, which took until December, were substandard. No reported attack by any Allied forces have come to light since the war to explain the loss, so all anyone can do is speculate as to what happened to her until she is finally found.