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. 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](https://en.wikipedia.org/wiki/Italian_auxiliary_ship_Olterra), 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](https://en.wikipedia.org/wiki/Siluro_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](https://en.wikipedia.org/wiki/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](https://en.wikipedia.org/wiki/Decima_Flottiglia_MAS) 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. |Date|Launched from|Result| |19 to 20 September 1941|Submarine Scire|Tanker Fiona Shell sunk, RFA Denbydale broken and beached, cargo ship Durham damaged, about 21,490 tons hit| |13 to 14 July 1942|Villa Carmela, near Algeciras|Twelve swimmers mined four merchant ships at anchor and got clear| |7 to 8 December 1942|Olterra|Three maiali sent against HMS Nelson, HMS Formidable and HMS Furious. All three failed. Visintini and Magro killed| |8 to 9 May 1943|Olterra|Pat Harrison, Mahsud and Camerata sunk or written off, roughly 19,375 tons| |3 to 4 August 1943|Olterra|Harrison Gray Otis, Thorshovdi and Stanridge hit, roughly 23,000 tons| 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. 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