In the shadowed waters of Gibraltar and beneath its tension-filled surface, a predator lay
hidden in plain sight.
Not the usual marine beast but a transformed Italian tanker, the Olterra harbored secrets
far more destructive.
As the world waged war, the seemingly derelict and abandoned vessel was really a hub of covert
operations.
A Trojan Horse in the heart of the British Navy's stronghold, the abandoned ship’s
deceptive exterior concealed a devastating surprise.
Interned within neutral Spain's port, she remained a silent observer, her true intentions
masked by her broken facade.
Yet within her belly, an army of Italian engineers and saboteurs prepared for a unique form of
warfare that would strike the enemy where they least expected.
La Decima
As World War 2 erupted, Italian dictator, Benito Mussolini had grand plans for the Mediterranean
Sea.
In his view, this expanse was his Mare Nostrum.
His confidence in defeating the Royal Navy was rooted in the might of the Royal Italian
Navy or Regia Marina.
An impressive lineup of four battleships, two 35,000-ton super-dreadnoughts, seven heavy
cruisers, twelve light cruisers, ninety destroyers, numerous motor-torpedo boats, and over 100
submarines all stood ready at the Duce’s command.
Another secret weapon in his arsenal was the Decima Flottiglia Motoscafi Armati Siluranti,
or simply La Decima.
Known for its innovative submarine warfare since World War 1, this unit had explosive
motorboats, midget submarines, leech and limpet mines, delayed action mines, and, perhaps
most uniquely, Maialis by 1940.
The Italian word for pigs, nicknamed for their unwieldy nature, Maialis were essentially
underwater chariots, where two men using breathing devices, would ride these electrically propelled
torpedoes, sitting behind a protective fairing and steer the vehicle toward the enemy ship.
The men would then attach the Maiali's warhead, which carried a timed fuse, onto the enemy
ship’s hull and escape just before the detonation.
Between September 24, 1940, and September 15, 1942, La Decima launched six submarine
assaults on Gibraltar Bay off neutral Spain.
These missions damaged numerous Allied vessels, but limitations quickly became evident for
the Italians.
A change in strategy led to a covert base in Spain, facilitated by Decima member Antonio
Ramognino.
His rented bungalow, Villa Carmela, overlooked a bay used by Allied convoys and became an
essential launchpad for attacks.
Amid these operations, Lieutenant Licio Visintini of La Decima conceived an ingenious plan:
a secret mothership for the Maiali.
They found the perfect ship for the task.
Underwater Espionage
Olterra, an Italian tanker built in 1921, was a sturdy ship capable of carrying nearly
5,000 tons over her 360-foot length.
Initially serving as an oil transporter, she was purchased by the Italian Navy in 1935
and frequently traveled between Mexico and Italy.
However, as Italy joined the war, Olterra found herself interned in the neutral Spanish
port of Algeciras in the strategically crucial Bay of Gibraltar, opposite a Royal Navy base.
For two years, she lay inactive, but her strategic location didn't escape Lieutenant Licio Visintini’s
eyes.
In early 1943, Lieutenant Visintini and a team of La Decima operatives, disguised as
civilian workers, gained control of the tanker by cleverly convincing Spanish authorities
they would salvage and sell the ship.
What followed were months of secretive work.
Disguised in official diplomatic bags, they smuggled parts for maintenance and repair,
even torpedo components.
Behind the facade of repair work, La Decima members turned her into a secret base.
Once a cargo vessel, her interiors were now meticulously equipped with maintenance workshops,
weapon depots, and an interior pool with an opening cut beneath the waterline for launching
torpedoes.
Externally, however, she kept her civilian guise.
The crew, appearing to be regular sailors overhauling the ship, performed their charade
well, keeping British and Spanish authorities unsuspecting of the true nature of their work.
When the modifications were complete, La Decima established the Squadriglia Ursa Major, the
special unit in charge of all Olterra operations.
With this, her transformation was complete by the end of autumn 1942.
No longer a simple cargo vessel, she was now a silent predator, poised beneath the calm
waters of Gibraltar, ready for her new mission.
First Incursion
The opportunity for attack presented itself on December 6, 1942, when a British naval
squadron, comprised of the battleship HMS Nelson, battlecruiser HMS Renown, aircraft
carriers HMS Furious and HMS Formidable, flanked by an array of escort units, glided into Gibraltar.
The convoy had just participated in Operation Torch and sought the relative safety of the
harbor.
Lieutenant Visintini swiftly organized a daring mission, entrusting three manned torpedoes
bearing two divers to infiltrate the seemingly impregnable Royal Navy defenses.
Visintini himself and Petty Officer Magro piloted the leading torpedo, with HMS Nelson
set in their sights.
2nd Lieutenant Cella and Sergeant Leone took charge of the second torpedo, targeting HMS
Furious, while Midshipman Manisco and Petty Officer Varini went after HMS Formidable in
the third.
On the early morning of December 8, the underwater assault crafts slipped out from Olterra's
belly and into the Mediterranean Ocean.
British base defenses, on high alert, vigilantly patrolled their waters.
Unbeknownst to the Italians, Lieutenant Lionel Crabb's bomb disposal unit patrolled beneath
dropped depth charges every three minutes as an added precaution.
Caught in this dangerous pattern, Visintini's torpedo met its fate at 2:15am.
A depth charge found its mark, imploding the vessel and claiming the lives of its crewmembers
as they attempted to bypass the harbor's steel defenses.
Next, Manisco's torpedo was exposed by a searchlight.
Pursued intensely, the crew chose to scuttle their craft, seeking refuge aboard an American
freighter before surrendering to the Gibraltar authorities.
Amid the chaos, the final manned torpedo slipped beneath the waters, eluding its pursuers.
Co-pilot Leone, however, vanished in the confusion and was never found.
Cella, uncertain of his location, emerged, expecting to be captured or interned, but
he surfaced to find the Olterra only a few feet away, much to his surprise.
Despite their capture, the two Italian divers maintained their ruse, asserting that a submarine
had launched the attack, keeping the secret Olterra intact.
The first operation was a failure, but the covert mission lived on.
Second Incursion
Following Visintini's unfortunate passing, Lieutenant Commander Ernesto Notari, former
world-freediving champion, emerged as a prominent figure within La Decima’s Ursa Major Unit.
After sneakily replenishing their ranks and arsenal with reinforcements from Italy, Notari
promptly set the stage for the next daring mission against the British Royal Navy,
Strengthened boom defenses that had claimed the lives of their comrades forced a shift
in strategy.
With logistic ships now playing a critical role following the Allied landings on Sicily,
the cargo-laden vessels around the naval base presented an irresistible opportunity.
By May 1943, decorated veteran Commander Borghese assumed command of La Decima.
The next assault was launched, taking advantage of a stormy night early that month.
Nottari and Petty Officer Ario Lazzari helmed a three-torpedo strike towards Gibraltar,
followed by torpedoes manned by Lieutenant Tadini and Petty Officer Mattera, and Second
Lieutenant Cella and Petty Officer Montalenti.
To keep Olterra under the radar, they targeted distant merchant ships.
The stormy seas made their task challenging, forcing a careful approach to plant limpet
mines on the hulls.
By the break of dawn the next day, the Italian torpedoes returned safely to their mothership,
leaving behind the American Liberty ship Pat Harrison and British freighters Mahsud and
Camerata, mined and primed for destruction.
Explosions shattered the tranquility of the rising sun.
As a result of the second immersion, the American transport was irreparably damaged, costing
a sailor's life.
Mahsud was partially submerged, but Camerata was lost entirely.
Italian secret service agents scattered diving equipment along the shore, misleading the
British into blaming combat swimmers.
The ruse lived on.
Third Incursion
Despite Italy standing on the brink of collapse as the summer neared, La Decima remained undeterred,
and the unit received the Medaglia d’oro in recognition of their valor on June 10.
The Ursa Major's third operation launched on the night of August 3, 1943, from the belly
of Olterra, aiming for three anchored transport ships.
Notari, partnered with Petty Officer Andrea Gianoli, led the charge.
However, while attaching explosives to a Liberty ship, their torpedo malfunctioned and dived
to a depth of 112 feet.
Emerging just feet from their target, Notari attempted to fix the issues and allegedly
escaped with the help of a school of porpoises.
Left behind, Gianoli was soon discovered and rescued.
The American Liberty Harrison Grey Otis, upon which they'd attempted to plant the explosive,
detonated moments before a British diver could investigate, resulting in one casualty and
eight injuries.
It was declared a total loss.
Simultaneously, the Norwegian Thorshøvdi was split in two, and the British Stanridge
sank in shallow waters, contributing to a devastating 23,000-ton loss of Allied shipping.
Olterra’s situation turned dramatically with Italy's surrender to Allied terms on
September 8, 1943, and the secret mothership’s clandestine operations ceased for good.
Despite suspicions, British authorities could only prove Olterra's role once they discovered
spare torpedo parts aboard the ship after the armistice.
The secret predator was moved to Gibraltar and her covert operations were fully exposed.
Finally, she was returned to Italy and was scrapped in 1964, ending her almost half a
century-long service.
After Italy's armistice with the Allies in September 1943, La Decima found itself divided.
One group, fueled by loyalty to Mussolini's Fascist government, joined the German-occupied
Italian Social Republic, relentlessly battling the Allies until the war's European theatre
concluded in May 1945.
Conversely, the other faction, loyal to King Victor Emmanuel III, integrated into the Italian
Co-Belligerent Navy, where they turned their prowess against the Axis powers.
The end of World War 2 didn't signify the end of La Decima's legacy.
Their spirit of audacity and innovation carried on, influencing Italy's post-war special forces.
Today, the Italian Navy's commando frogman force, COMSUBIN, proudly traces its origins
back to La Decima, upholding the tradition of special naval warfare operations.
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