What does the 'U' in U-boat stand for and how many of them are left?

Few naval vessels have developed as enduring of a legacy as German U-Boats, but what does that name actually mean?
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The real Das Boot - The U-boat patrol behind the most famous submarine story ever told

U-96 was already one of Germany’s most successful Type VII submarines by the time war correspondent Lothar-Günther Buchheim came aboard in 1941. Under Captain Heinrich Lehmann-Willenbrock, the boat ...