Italian manned torpedoes and commando frogmen from the Decima Flottiglia MAS were brought to Algiers aboard the Perla-class submarine Ambra.

The participating commandos were captured after setting limpet mines which sank two Allied ships and damaged two more.

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.

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.