On 4 December 1942, Ambra, a submarine of the Italian Royal Navy (Regia Marina), left the naval base of La Spezia, carrying three manned torpedoes and 10 commando frogmen. Air reconnaissance had discovered that the port of Algiers was crowded with Allied cargo ships, so the Italian High Command decided to launch an operation involving both human torpedoes and combat swimmers carrying limpet mines. On the evening of 10 December, Ambra reached Algiers at a depth of 18 metres (59 ft). One of the swimmers was employed as scout on the surface, and he guided the submarine toward a position 2,000 metres (6,600 ft) from the southern entrance to the harbour. He spotted six steamers at 21:45, and informed the presence of targets to Ambra by phone. The other swimmers and the manned torpedoes begun to emerge at 23:45 after some delay. The observer reported an intense reaction from the harbour defences. The submarine awaited to recover the operators until 03:00, an hour after the original time set. Then the scout swimmer was recalled on board and Ambra departed back to La Spezia. Meanwhile, at 05:00, the explosions started to rock the freighters. The Norwegian Berta (1,493 tons) was sunk, while Ocean Vanquisher (7,174 tons), Empire Centaur (7,041 tons) and Armatan (4,587 tons) were heavily damaged. The American landing shipLSM-59 became stranded on the beach. Sixteen Italian divers were captured.
