Gibraltar was one of the more strategically important bases for the Royal Navy in the Second World War. With it, the Mediterranean was completely sealed up and contained. The Bay of Gibraltar also gave a nice sheltered area for shipping to rest on its way to somewhere else. Think about ships heading up and down the Atlantic, and where the next guaranteed friendly port might be, possibly not until South Africa or Ascension Island? The Bay of Gibraltar is only about 8km wide, on one side you have Gibraltar, on the other the Spanish port of Algeciras. Usually, during the war merchant ships anchored up to about 1km from Gibraltar in the bay. The depth of the bay can be up to 400m, although a lot of the bay is much less than that. It was over one of these much shallower parts that on the 10th of June 1940 the Italian ship Olterra was berthed. On the declaration of war, the Olterra was sunk, how exactly no one is sure. The most common story is a raid by British commando's, but that is not mentioned anywhere else, and frankly, I doubt the British had the raiding forces in place that early. Equally, as we'll see, the damage was rather negligible. Another story is that it was scuttled by her crew is something I find much more credible. Especially as when she had settled on the seabed, she still had parts of her above water, as two Italians and a Spanish guard remained on board to maintain Italy's ownership over her.
The Italians then decided on a new approach. They hired a villa that was just 4km from the Gibraltar harbour entrance. From here they were able to dispatch frogmen to attack shipping, sinking five more merchants in short order.
A picture, taken in 1942, from behind Gibraltar looking across the bay to Algeciras.
Then a new plan was hatched. The Olterra was raised and moved to Algeciras. Under the cover of refitting and repairs modifications were made to the ship to include a secret underwater hatch and a hangar deck for Maiales. The equipment needed to operate the Maiales from the ship was transported across Spain, as spare parts, and the crews also posed as workers. To all intents and purposes the Olterra seemed to be undergoing repair and refit after sitting on the ocean floor for so long. The British did have some vague suspicions about all this activity, as they could clearly see the ship under refit. However, they never seemed to link it to the idea of a mother ship.
At the end of 1942, Force H sailed into Gibraltar Harbour. The Italians had become operational only a short while before and they decided that the battleship HMS Nelson, and the carriers HMS Formidable and HMS Furious would be their first targets. On the 8th of December three Maiales floated out of the underwater hatch and set off for the warships. However, the target ships were actually inside Gibraltar harbour. The British were aware of the likelihood of an underwater attack and had small depth charges they'd drop to cover the harbour entrance. By sheer random chance one of the depth charges scored a direct hit on one of the Maiales killing the crew.
A similar fate occurred to the third torpedo. Spotted and chased they had almost run out of air, so the crews scuttled their craft, and surrendered. They claimed they had been launched by submarine.
It had become clear that Gibraltar harbour was too well defended. However, the mass of transport shipping was still vulnerable. On the night of the 8th of May 1943 another sortie was carried out, this was aimed at the ships as far away as possible, to give the deception the attack was coming from the sea. Three ships were attacked, and all three sunk or so badly damaged they were written off.
Loitering under the target ship the co-pilot was working to attach the mine, when the Maiales malfunctioned and crashed dived. Suddenly the dive was reversed and the Maiales sprung to the surface. This could very well have incapacitated the pilot who was still in place, and indeed seems to have left him almost unconscious. Unable to submerge again, barely conscious, the pilot left on the surface at full speed heading back towards the Olterra. By sheer blind luck a school of porpoises was heading in the same direction, and the splashes and shapes of them moving covered his escape.
Back at the target ship the co-pilot finished attaching his mine. Then he clung onto the rudder of the ship for two hours, before he judged it was too late for the British to remove the charge, then called for help. Once rescued the British were certain there was a mine and called for a bomb disposal diver. Before he could start his dive, the mine exploded sinking the third ship. The following month the Italians signed an armistice with the Allies, and the Olterra's mission was over.
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