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An experimental underwater repeater recently installed in one of The Western Union Telegraph Company's transatlantic nonloaded telegraph cables increased the operating speed of the cable from 50 words per minute to 167 words per minute. The repeater is located 170 miles at sea in a depth of 270 fathoms which places it beyond shallow coastal waters where disturbance levels are high. The cable beyond the repeater is in deep water and free from disturbance so that signals alone are amplified and the signal-to-noise ratio at the terminal is greatly increased. The 3-stage amplifier and signal-shaping networks are mounted in a pressure-equalized steel case. Power for the repeater is supplied by rectifiers at the cable terminal. The repeater includes a switch, under control of the terminal, by means of which spare vacuum tubes can be substituted or the cable can be cut directly through for operation without repeater.