Italian Manned Torpedos
During the early 1940s, Gibraltar’s harbor became a strategic focal point for the Italian Navy. Protected by the British and crowded with Allied warships and merchant vessels, it offered a tempting target for sabotage. In response, the Italians created an elite naval unit known as the Decima Flottiglia MAS. These men specialized in unconventional underwater warfare, including the use of manned torpedoes called “maiali,” or “pigs,” due to their clumsy handling.
The earliest operations against Gibraltar involved deploying these human-guided torpedoes from submarines such as the Sciré. On 10 September 1941, three two-man crews piloted their torpedoes into Gibraltar Harbor under the cover of night. Each team navigated underwater to its assigned target, attaching limpet mines to the hulls of anchored ships. As the operators retreated, the charges exploded hours later, destroying the tankers Denbydale and Fiona Shell, along with the cargo ship Durham. The crews managed to swim to neutral Spanish territory and eventually returned to Italy.
Although the attack was a success, it exposed the limitations of launching from submarines: the danger of detection, mechanical unreliability, and operational constraints. The Italians needed a safer and more permanent base for continued operations. Their solution was as daring as it was ingenious.
They covertly converted the Italian tanker Olterra, which was moored at the Spanish port of Algeciras across the bay from Gibraltar. While officially interned and inactive, the Olterra was secretly modified below deck. A hidden compartment was created in the bow, with a concealed watertight hatch beneath the waterline. From here, Italian frogmen could discreetly launch manned torpedoes directly into the harbor, avoiding the risks of long underwater approaches from a submarine.
Operations from the Olterra began in 1942. The first of these saw Italian divers swim across the bay under cover of darkness, attaching explosives to ships docked in the harbor. Several ships were damaged or destroyed in these missions. The British suspected sabotage but had no idea where the attackers were coming from.
In July 1942, a coordinated assault led to the sinking of multiple freighters, including Meta, Empire Snipe, Baron Douglas, and Shuma. The use of the Olterra enabled the Italians to strike quickly and retreat undetected. Later that year, a more ambitious attempt aimed at British warships was launched. Although it failed due to strong defenses and bad luck, it further demonstrated the persistence and fearlessness of the Italian crews.
The most dramatic success came in 1943. On the night of 8 May, three teams departed the Olterra aboard manned torpedoes and entered Gibraltar Harbor. They successfully planted charges that destroyed the American Liberty ship Pat Harrison and the British freighters Mahsud and Camerata. The Italian saboteurs escaped to Spain. In August, another similar raid resulted in the sinking of three more vessels: the Norwegian ship Thorshøvdi, the Liberty ship Harrison Grey Otis, and the British freighter Stanridge.
These raids caused significant disruption to Allied logistics and forced the British to strengthen harbor defenses further. While not all missions succeeded, and some operators were killed or captured, the effectiveness of these operations surprised Allied commanders and demonstrated the boldness and innovation of the Decima Flottiglia MAS.
As for the Olterra itself, after serving as this covert base for underwater attacks, it remained moored in Algeciras throughout the war. Because Spain maintained a position of official neutrality, the Olterra was never seized or destroyed by Allied forces. After Italy surrendered in 1943, the ship was eventually abandoned by its crew and left inactive. Post-war, the Olterra was repaired and returned to commercial service as a merchant vessel, its secret wartime role largely forgotten for many years.
The use of the Olterra as a covert base remains one of the most audacious and creative acts of naval sabotage in history. Italian frogmen, through a mix of stealth, courage, and ingenuity, managed to inflict considerable damage within one of the most heavily guarded harbors in the world. Their operations in Gibraltar stand as a remarkable chapter in the history of underwater warfare.
