Buster Crabb, The Silent Enemy And The Tanker That Attacked Gibraltar From Spain

25 August 2026 Last checked 2026-08-25

Italian frogmen hit Gibraltar harbour from a hatch below the waterline of a tanker moored in Spain. The true story, and what is left to see today.

The most damaging attacks on Gibraltar harbour in the Second World War came out of a hatch cut about six feet below the waterline of a rusting Italian tanker. The tanker never moved. It sat in a neutral Spanish port five miles across the bay, in plain view of the Rock, for the better part of a year.

The officer sent to deal with them was a 33 year old chain smoker called Lionel Crabb who could not dive when he arrived. He learned in the water he was defending, wearing overalls and plimsolls. Most people who know his name know it for the wrong reason, which is that he vanished in Portsmouth Harbour in 1956 and nobody has ever explained why.

The tanker that was really a submarine base

On 10 June 1940, the day Italy entered the war, the tanker Olterra was anchored off Algeciras on the Spanish side of the bay. Her crew scuttled her rather than let the Royal Navy take her. She was 5,000 gross register tons, built on the Tyne in 1913 as the Osage, and by any normal reading of events that was the end of her.

It was not. In 1942 the Decima Flottiglia MAS, Italy's naval special forces unit, raised her on the stated pretext of preparing her for sale and had her towed into Algeciras. Italian navy personnel posing as civilian dockyard workers gutted the holds and boiler rooms and rebuilt them as a workshop. The unit inside was called Squadriglia Ursa Major. The conversion is set out in the ship's record, down to the observation post fitted on the forecastle so crews could watch Allied shipping arrive.

The workshop assembled maiali, the manned torpedoes whose Italian nickname translates as pigs. A Siluro a Lenta Corsa was 6.77 metres long, weighed 1.8 tons, carried two men sitting astride it and a detachable 260 kg warhead, and did 3 knots flat out with a range of about 15 nautical miles. A sliding hatch below the Olterra's waterline let the crews ride out submerged and come home the same way. She stayed at her mooring throughout.

Look at a map and the nerve of it becomes obvious. The Bay of Gibraltar is roughly 10 km long and 8 km wide, so Algeciras sits about five miles from the Gibraltar waterfront. British officers looked straight at the Olterra for months. Several of them, presumably, wondered why a derelict tanker needed so many visitors.

She was not even the only Spanish launch point. On the night of 13 to 14 July 1942 a dozen swimmers from the same unit left a rented house near Algeciras that became known as the Villa Carmela, swam into the harbour and mined four merchant ships lying at anchor. Italian accounts say seven of them were picked up by Spanish carabineros on the way back and handed to the Italian consul in Algeciras rather than to the British. That detail says as much about Spanish neutrality in 1942 as any treaty text does.

What the frogmen actually cost the Allies

The figure usually cited for the Olterra raids is about 42,000 tons of Allied shipping sunk or written off across six merchant ships, achieved by a ship that never left a neutral harbour. As special operations go the ratio of cost to effect is close to unmatched, and almost nobody in Britain has heard of it.

There is a pattern in that table the popular retelling misses. Every attempt on a warship failed. Nelson, Formidable and Furious were all attacked and none was touched. What the frogmen actually sank was merchant shipping riding at anchor, away from the concentrated defences around the fleet. RFA Denbydale, a fleet oiler, was the closest they came to a naval target, and she was patched up and spent the rest of the war as a hulk at Gibraltar. The defence held where it was thickest and gave way at the edges.

The man sent to stop them

Crabb was born on 28 January 1909 and arrived at Gibraltar in October 1942, appointed to HMS Cormorant as a mine and bomb disposal officer. He was not a diver. He was, by most accounts, an unremarkable swimmer. He was also the person available, which is how a great deal of wartime specialism actually got assigned.

The Underwater Working Party he joined, under Lieutenant Bill Bailey, had almost nothing. They breathed from Davis Submerged Escape Apparatus, built for getting out of a sinking submarine rather than for working underwater. They wore overalls instead of suits and plimsolls instead of fins. Their method for finding a limpet mine on a hull at night was to swim along it and feel for one. The Minewarfare and Clearance Diving Officers' Association account of his service is the most careful summary in print.

On the night of 7 to 8 December 1942 the Olterra sent three crews against the fleet. Lieutenant Licio Visintini and Petty Officer Giovanni Magro were killed, most probably by small charges dropped over the side by harbour defence patrol boats, a tactic generally credited to Crabb. When the bodies were recovered, Crabb and Leading Seaman Sydney Knowles took the dead men's swim fins and started using them.

That is the moment the whole story turns on. The Royal Navy did not issue fins in 1942. The British learned to work underwater from the kit of the men they had just killed, and the Navy's clearance diving branch grew out of that improvised working party rather than out of any pre war doctrine.

Crabb and Leading Diver David Bell were each awarded the George Medal on 25 January 1944. Crabb was promoted to lieutenant commander, became Principal Diving Officer for northern Italy clearing mines from Livorno and Venice, and was appointed OBE in December 1945. His service record is unusually well attested for a man whose ending is not.

After the Italian armistice on 8 September 1943 the Olterra's secret was finally exposed. Crabb's team got aboard, found the workshop, the underwater hatch and enough spare parts to assemble a complete manned torpedo, and put one together. They called it Emily.

The Silent Enemy, and where it is wrong

The Silent Enemy reached cinemas on 4 March 1958. William Fairchild wrote and directed it from Marshall Pugh's 1956 book Commander Crabb. Laurence Harvey plays Crabb and Michael Craig plays Knowles. It was shot in England, Malta and Gibraltar, so some of what stands behind the actors is the Rock itself.

It is also wrong in ways worth knowing before you watch. The Italian craft on screen are British Chariots standing in for maiali. Crabb's route into diving is compressed into a few scenes when in reality he spent months on mine disposal first. The Monthly Film Bulletin said at the time that the film failed to give a convincing picture of Crabb, and it was right. Watch it for the underwater photography and the Gibraltar exteriors. Do not take the history from it.

Gibraltar has form as a film location and the frogman story is not the only one you can walk. The Rock appears in two James Bond films, the burial at sea sequence shot in the harbour in 1966 and the opening of The Living Daylights in 1987, and most of those locations are still reachable.

Why the name is famous, and it is not Gibraltar

On 19 April 1956 Crabb, then 47, dived in Portsmouth Harbour to inspect the hull of the Soviet cruiser Ordzhonikidze, which had carried Nikita Khrushchev and Nikolai Bulganin to Britain on a state visit. He was working for MI6. He did not surface. The Admiralty put out that he had been lost during trials of underwater apparatus in Stokes Bay, which was not true and was not believed.

On 9 June 1957 fishermen recovered a body off Pilsey Island in Chichester Harbour, in a Pirelli suit of the type Crabb wore, missing its head and both hands. Knowles, who knew his scars, said it was not him. A pathologist re examining the remains found scarring that matched. The coroner recorded an open verdict later that June.

Here is the honest position, and it is worth stating plainly because most pages about Crabb will not. Nobody writing today knows what happened. Cabinet papers on the case are reported to be closed until 2057. In 2007 a Russian diver named Eduard Koltsov claimed on camera that he had cut Crabb's throat, and a journalist from the Russian military newspaper Krasnaya Zvezda publicly doubted the account. Anyone offering you a confident answer is guessing.

What is actually left to see here

Very little, and you should know that before you build a day around it. The Olterra was broken up in 1961 at Vado Ligure and what survives of her sits in an Italian naval museum at La Spezia, not in Gibraltar. The harbour is a working commercial port. The moles are not somewhere you can wander.

We could not confirm that the Gibraltar National Museum carries a permanent display on the frogman war, and we would rather say so than invent one. If that is your reason for coming, email the museum and ask before you travel. It is a five minute job that saves a wasted morning.

What you can do costs nothing. Stand on the western waterfront, anywhere between Ocean Village and Rosia Bay, and look across at Algeciras. That water is the whole story. Eight kilometres of it, in the dark, on a 1.8 ton machine doing 3 knots, with 260 kg of TNT under your feet and depth charges going off somewhere ahead.

For the wider view you want height. The cable car has been shut since November 2025 for a full rebuild and is expected back in 2027, so the ways up are a licensed taxi tour or your own legs. From the Upper Rock the geometry of the bay makes immediate sense in a way no map manages, and you can see plainly why Gibraltar exists as a place at all.

One more thing changes how the story reads. The town below the harbour was largely empty. Most of Gibraltar's civilian population had been evacuated in 1940 and did not start coming home until April 1944, scattered to London, Madeira and Jamaica. Sailors, soldiers and the small number of essential workers allowed to stay. Nobody watching from a balcony.

The British learned to fight underwater from the fins of the men they had just killed. That is not a heroic story. It is a truer one.

If you are coming to look at the harbour

The northern end of Gibraltar is the working end, and it is where Victory Suites is. We are on Devils Tower Road, about three minutes from the airport and roughly ten minutes on foot from the Spanish frontier, with 100+ apartments and a full kitchen in every one. A fair share of our guests are merchant seafarers rather than tourists, which is the same trade this entire story turns on, eighty odd years on. If you are here for shipping rather than sightseeing, our shore leave guide is the practical companion to this piece.

Worth holding in your head while you walk to Spain in ten minutes: the men in this story took a whole night to cover the same bay, underwater, at walking pace. Book direct or through any of the 300+ booking channels we list on, and message us for the ten minute version of this history. Somebody on the team will have an opinion about the film.