The newest Submariners have special ratcheting clasps which offer a very precise fit for optimal comfort.

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The government also brought in Chile's navy, whose submariners have experience working at great depths in confined spaces.

ECONOMIST: Chile's mine rescue

Our investigations took us to St Petersburg and the Soviet Submariners Veterans' Society via the National Security Archive in Washington DC, where Svetlana Savranskaya, the director of the Russian archives, told us an incredible story.

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