An electronic version of the Cardan Grille, a predetermined set of frequencies would be established between sender and receiver, as though each one had the top card with slots that could be placed over the coded message: “Sir John regards you well and spekesagain that all as rightly avails him is yours now and ever. May he ‘tone for past d’layswith many charms.”
Once the “receiver,” the torpedo received the message, it could decipher it electronically by selecting the proper frequency slots to isolate the relevant parts: “Spain sails in May. To arms.”
Cardan Grill Example – Decoder Card and Encoded Message
