From the National Archives:
As this telegram shows, it was not always necessary to encrypt an entire message. Sometimes just a few key words or phrases were enough. Confederate Gen. Joseph E. Johnston sent this telegram to Secretary of War James E. Seddon on June 16, 1863. The decryption shows what he was trying to hide: details advocating an invasion of Kentucky and his proposals to enlarge Gen. Braxton Bragg’s area of responsibility.