U-Boats used the blinking lights of signalling lamps to communicate in Morse Code.

The lamp had to be pointed directly at its target in order to be seen, but this narrow beam reduced the chance of being spotted by enemy ships. Radios allowed U-Boats to communicate over much larger distances, but signal lights were still vital communications equipment. Donated to the Canadian War Museum by A.R.M. Lower, a Canadian officer in the Royal Navy and later a prominent Canadian historian, the lamp is likely from U-117, which surrendered at Harwich, England on 21 November 1918, ten days after the Armistice.

Signalling Lamp, German
CWM 19740259-009