In a lifetime’s career in marine salvage, Alec Crawford has explored wrecks from remains of the Spanish Armada to the SS Politician, the vessel made famous in the film Whisky Galore – and also the White Star Liner Oceanic, which, when built in 1899, was the biggest and most luxurious ship in the world. Widely regarded as an ‘undiveable’ wreck, lying somewhere off the remote island of Foula, it was one of the ultimate underwater challenges.