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Meet the only man alive who has been to the deepest ocean

23 February 2012 Last updated at 14:05 GMT

On 23 January 1960, two explorers, US navy lieutenant Don Walsh and Swiss engineer Jacques Piccard, became the first people to dive 11km (seven miles) to the bottom of the Mariana Trench.

As a new wave of adventurers gear up to repeat the epic journey, Don Walsh tells the BBC about their remarkable deep-sea feat.