Morse Code

Morse code, transmitted by flashing light, is recognized in the International Code of Signals for letter-by-letter spelling when flag or voice will not serve. A few groups carry standing meaning: the distress signal is SOS (… — …) sent as one run-together group; the letter U (..-) flashed by light warns ‘you are running into danger.’ At sea the daylight signaling lamp (Aldis) sends Morse; the dot is the unit, the dash three units, the inter-element gap one unit, and the inter-letter gap three units.