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Submarine signaling
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Current converting device
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System and apparatus for submarine signaling
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Electric signalling circuits
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Method and apparatus for sound transmission
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Direction finding
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Electric compensator
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Sound receiver and transmitter
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Apparatus for measuring distance
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Apparatus for measuring distance
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Submarine signaling
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Submarine signalling apparatus
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Sound receiving apparatus
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Submarine sound reception
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Method and apparatus for sound producing
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Sound-receiving apparatus
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Method and apparatus for sound transmission
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Method and apparatus for distance and direction measurement
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Apparatus for draining sound tubes
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Method and apparatus for measuring distance
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