There is a type of Cipher common among the militaries, called an ottendorf cipher, a type of book cipher.
"The Ottendorf Cipher is a form of Book Cipher. Its ciphertext is made up of numbers in groups of 3, and these numbers correspond to positions in a book (or other type of text). Most often the numbers refer to Line, Word, and Letter.
To encode a message, the encoder needs only to utilize a piece of text written within a book (or other location) to indicate letters to create a message. The decoder needs to then know the ‘Key’ (the text) of which to apply the numbers of the ciphered message to."
https://mysteriouswritings.com/mw-codes-ciphers-and-puzzle-series-the-ottendorf-cipher/