noun
EXAMPLES FROM CORPUS
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Mina got the tip-off just in time and they became U-boats, went underground.
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The convoy was attacked by U-boats during the night of March 16-17 and 12 ships, including Southern Princess, were sunk.
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Then the U-boat just left them on the open seas.
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There is no mention of U-boats or the Luftwaffe.
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They acted as bait and, once a U-boat surfaced, could out-gun her.
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They already seen U-boats off Nova Scotia.
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You know enough about that to know the difference between a whale and a U-boat ?
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You know what a U-boat looks like, boy?