CIPHERS. A signal cipher is a method of or key to secret signaling understood only by those concerned. In the presence of the enemy the necessity for its use is apparent, and in order to secure secrecy it must frequently be changed.
Naturally there are countless forms and systems of ciphers. Among these is the signal disk, which is a device for readily enciphering and decipher ing a message. It consists of a small disk of cardboard or other material, on which are writ ten or printed the letters of the alphabet in irregular sequence and arranged around the cir cumference of the disk. These letters are so placed that when the disk is properly held all the letters are upright. On this small disk are also printed those combinations of letters which frequently occur in words, as 'tion, 'ous,' etc., and a sign to mark 'the end of the word.' On a larger disk are written or printed, arranged around its circumference in the same manner, either the letters of the alphabet or the symbolic numbers of signals which are to be used. The
disks are fastened concentrically together in such manner that one may revolve upon the other and that they may be clamped in any position. They are of such size that when so fastened the letters, etc., upon the inner disk will cinch appear close to and directly opposite one of the signal combinations upon the outer disk.
The figures '1' and '8' are sometimes used in stead of the figures '1' and '2' to symbolize the elements 'one' and 'two,' because the figure '8' is upright in most positions of the disk. Having a disk so arranged and clamped. it will be clearly understood by any signalist that, so provided, lie has before him an alphabetic code with every letter opposite its signal symbols. And he will comprehend that, by referring to the disk, he can transmit a message without the study of any par ticular code and can transmit it in secret signals or cipher by moving the disks upon each other.