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Measurements have been made of the slant ranges over which light pulses were transmitted from a submerged submarine to an aircraft off the coast of Key West Florida. These experiments were performed as part of an investigation of the use of light for identification and communication between submerged submarines and aircraft. At night during a full moon, slant ranges of 15 and 14 miles were measured when the receiver was at altitudes of 5000 and 2500 feet, respectively, and when the light source was 50 feet below the sea surface. Even with the light at a depth of 100 feet, light pulses could be detected at a slant distance of about 11 miles from an altitude of 2500 feet. These data were gathered using a submergible transmitter which emits high intensity one microsecond flashes of light in an 11 degree beam. A very sensitive photoelectric receiver detected the light pulses during ambient illumination from a full moon when the pulses could not be seen by eye.