During the Atlantic Convoys, radio silence was imperative to avoid detection by the German submarine wolf packs. Covert coded communications were made by transmitting a series of letters by light in morse code, from bridge wing to bridge wing. Message such as speed orders, alterations of course, submarine intelligence and even correspondence chess moves were relayed in this way in total silence.
To enable rapid interpretation of the flashing morse light on a darkened bridge, a morse crib chart was created similar to this one, and used to quickly determine the morse lettering and applicable coded order.
To use, shaded squares are dots and light squares dashes. Starting from the top A = • – R =• – • Z =– – – •
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Kraken Offshore 