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Operation Ursa Major, an Italian operation to sink allied shipping at Gibraltar

Operation Ursa Major, an Italian operation to sink allied shipping at Gibraltar during WWII

By Nick Nutter | Last Updated 15 Mar 2022 | Gibraltar | History
Buster Crabb

Buster Crabb

During WWII the Italians devised a daring plan designed to threaten Allied Shipping in Gibraltar Bay off the shores of neutral Spain. The operation was conducted with all the panache associated with Italians.

The Olterra

Members of Decima Mas

Members of Decima Mas

Built in 1913, on Tyneside in the UK for a German company, the tanker Osage was sold to the Standard Oil Co, in New York in 1914 and renamed Baton Rouge. In 1925 she was again sold, this time to the European Shipping Co Ltd of London and renamed Olterra. As the Olterra she passed through the hands of the British Oil Shipping Co Ltd and in 1930 was bought by Andrea Zanchi in Genoa. On the 10th June 1940, when Italy declared war on France and Britain she found herself in Gibraltar Bay. The shipping records of the builders, Palmer’s Ship Building and Iron Co Ltd, indicate that she was sabotaged and sunk by British commandos close to the Algeciras shore.

The Olterra was taken over by a group of Italian commandos. She was re-floated, taken to Algeciras docks and used as the headquarters for the most audacious, and successful, Italian undercover operation of the war, code-named Ursa Major.

Decima Flottiglia MAS

HMS Formidable

HMS Formidable

If there was one aspect of warfare that the Italians excelled at it was underwater, particularly their use of human torpedoes and combat swimmers. Human torpedoes were developed by the Italians to approach enemy ships underwater and unseen. They were a torpedo shaped vessel that contained an electric motor and a detachable warhead. One or two crew members, equipped with diving gear, sat astride the machine to control it. The Italians called them maiale (pigs), because they were difficult to control.

Shipping in the harbour at Gibraltar was an obvious target for the Decima Flottiglia MAS, the Italian ’10th Assault Vehicle Flotilla’, an elite commando swimming unit of the Italian Royal Navy.

HMS Nelson

HMS Nelson

Between September 1940 and 15th September 1942 they carried out three attacks using human torpedoes launched from a submarine. Meanwhile the commander of the Decima MAS conceived a daring scheme.

The Villa Carmela

Otlerra showing divers hatch

Otlerra showing divers hatch

He realized that with a base on Algeciras Bay underwater attacks on shipping at Gibraltar would be more effective. A member of the Decima, Antonio Ramognino who had a Spanish wife, rented the Villa Carmela which was situated on a small hill alongside the Arroyo Cachon at Puente Mayorga on the north side and overlooking Gibraltar Bay and the western side of ‘The Rock’ including the harbour and anchorages. That base was ready by July 1942 and, together with a forward observer on the still sunken Olterra, frogmen sank or damaged five merchant ships using limpet mines in just three months.

The Olterra refit

An Italian human torpedo

An Italian human torpedo

At the same time as these missions were being planned and executed another member of Decima MAS, Lieutenant Licio Visintini was in charge of a team of commandos disguised as Italian civilians. Under the pretext of repairing and selling the Olterra to a Spanish buyer they raised the ship and towed it into Algeciras harbour.

There the ship underwent a refit. An observation post was created on the forecastle whilst inside the ship the holds were converted into workshops for the assembly and maintenance of the human torpedoes, or maiale, pigs, as the Italians called them. The motorized pigs were smuggled onto the ship disguised as spare parts and other pieces of nautical equipment. Finally a hatch was cut through the hull beneath the waterline so that the torpedoes could be launched and recovered in secret.

Targets Nelson, Formidable and Furious

By December 1942 the Olterra, her torpedoes and crews were ready for their first attack which turned out more ambitious than they could have dreamt of. On the 6th December, after taking part in Operation Torch, the landings in French Morocco and Algeria, Force ‘H’ including the battleship HMS Nelson, battlecruiser HMS Renown, aircraft carriers HMS Furious and HMS Formidable together with support ships entered Gibraltar.

Visintini and his men set off on three manned torpedoes from Olterra the night of the 8th December. Their targets were the Nelson, Formidable and Furious.

Following the attacks earlier in the year the allies had implemented a number of measures to deter or foil attacks on shipping from beneath the waves. A Lieutenant Lionel Crabb, the famous ‘Buster Crabb’, was in charge of an underwater demolition team. Motor boats were deployed to drop small depth charges every three minutes, the charges were large enough to kill or injure a man and damage a human torpedo but not large enough to damage large ships.

The first human torpedo, driven by Visintini and his Petty Officer Magro, was hit by one of the depth charges. The bodies of the crew were recovered later by the British and given a burial at sea with full military honours.

The second torpedo, manned by a Second Lieutenant Cella and Sergeant Leone, was spotted on the surface by a searchlight but managed to slip beneath the water and avoided the submarine chasers that were by now searching the anchorage furiously. Leone was washed from the torpedo and his body was never found but Cella managed to return to the vicinity of the Olterra where he scuttled his craft and returned to his base. The craft was later brought back into the Olterra and repaired.

The third torpedo, manned by Midshipman Manisco and Petty Officer Varini, was also caught in searchlights and chased. Running out of air they scuttled their craft and took refuge on an American freighter and later gave themselves up to allied troops on Gibraltar. When interrogated they maintained the attack had been launched from a submarine.

Undeterred the Italians re-supplied the Olterra with men and torpedoes. A Lieutenant Notari took charge of the Olterra group, codenamed Ursa Major.

A Dark and Stormy Night

On the 8th May 1943, a dark and stormy night as it transpired, three human torpedoes set off from the Olterra. Their targets were allied freighters anchored as far as possible away from Algeciras. Second Lieutenant Cella, the only one to make it back from the first attack, was in charge of one of the maiale. This time the teams were more fortunate. They successfully mined three freighters, an American liberty ship, Pat Harrison that was severely damaged and became a total loss, the British freighter Mahsud which sank to the bottom with its upper works still visible and the freighter Camerata which sank outright. All three human torpedoes and their crews returned safely to the Olterra. A stunning success. To mislead the allies into thinking the attack had been made by combat swimmers an Italian team scattered scuba gear along the Spanish shore.


The Medaglia d’oro

The team from the Olterra continued to plan and execute attacks against allied shipping. In June 1943 the entire Ursa Major team was awarded the Medaglia d’oro for their deeds but the war was not going well for the Axis powers.

On the 13th May the Axis powers in North Africa had surrendered. The allies had invaded Sicily on the 19th July and were preparing to attack the Italian mainland.

On the 25th July Mussolini was removed from power, Italy was on the brink of collapse and negotiations towards a peace treaty between Italy and the Allies had allready, tentatively, started.

Notari was determined to fight to the end.

The Final Mission

On the night of 3rd August 1943 the Ursa Major team made their last foray. Notari led three manned torpedoes and successfully reached the anchorage undetected. He unattached his mine beneath a liberty ship, the Harrison Grey Otis. Whilst his crew member, Petty Officer Giannoli, was working to attach the mine the torpedo malfunctioned and crash dived to a depth of 34 metres. It then careered to the surface with Notari half conscious. Having lost Giannoli and with his craft damaged Notari made his escape at full speed on the surface, his wake covered by a troop of dolphin that fortuitously accompanied him. Giannoli meanwhile had attached the mine and climbed onto the ship’s rudder. After two hours he called for help and was taken aboard. A member of Buster Crabb’s team was called to search the hull for mines but the mine exploded before the diver entered the water.

The Otis was declared a constructive total loss. The other two crews had also done their work and the Norwegian ship Thorshovdi and the British Stanridge were sunk.

Armistice of Cassibile

Just one month later, on the 3rd September 1943, the Armistice of Cassibile was signed between Italy and the Allies, ending Italy's part in the war.

Lieutenant Notari and his Ursa Major team finished their war on a high note


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  • Rob - 10 Apr 2019
    the changing format of the photos make it difficult to read your good text
    • Nick Nutter - 12 Apr 2019
      Sorry, I have removed all nut one image.
  • Rob - 10 Apr 2019
    paul kemp in his book underwater warriors p41 writes " Olterra had been scuttled by her Italian crew on the outbreak of war, but had been refloated by the Spanish & secured inside the breakwater at Algeciras. A guard consisting of a corporal & 4 privates of the Guardia Civilia was placed on the ship to prevent any unauthorised personnel boarding her. In March 1941 members of Olterra's original crew, including Paola Denegri , the chief engineer, reboarded the ship to act as a care & maintenance party. ...... Visintinni arrived on board Olterra on 27th June1942 with civilian papers indentifying him as Lino Valeri, the prospective first officer of the ship. He brought with him 3 technicians & a medical technician." and lots more about the Olterra & the people & it's operations,
    • Nick Nutter - 12 Apr 2019
      Interesting. The shipbuilders records may well be incorrect.
  • Philip Crawford - 8 Apr 2019
    Hi Nick:
    Interesting article. I have a Panerai watch which is a recent homage to the Decima MAS. Panerai built specially-commissioned diving watches to the teams and the one I have has an embossed outline of one of the torpedo-shaped mini-subs with two commandos sitting astride it underwater. It must have been a particularly hazardous occupation! The original watches were big, varying from 47mm to a massive 60mm in diameter, and used pocket-watch movements from Rolex and Angelus. I am currently building a replica using where possible contemporary parts. The case is made, and I have found an original movement in Peru (would you believe) which is currently being restored for me by a watchmaker in Chile! An original watch recently sold at auction for £65,000.
    The 1958 film The Silent Enemy was based on Lionel Crabb and his team who operated to foil the activities of Italian frogmen in Gibraltar.
    • Nick Nutter - 8 Apr 2019
      Hi Philip, Thanks for the comments. It would be great if I could have an image of the watch when it is finished and I will add it to the article images.

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