Dictionary Cipher for the CSS Florida

As the Confederate commerce raider Florida prepared for what would be a legendary cruise, Secretary of the Navy Stephen Mallory sent instructions to her captain, James Maffitt. Included were these interesting instructions to encode messages sent back to America, using a book cipher. He wrote:

Obtain at Mobile two uniform copies of any small English lexicon or dictionary, one to be retained by you and the other to be sent to the Department. Whenever in your letters or dispatches a word is used which may betray what you may desire to conceal, instead of using that word write the numbers, in figures within brackets, of the page where it is to be found, and also the number of the word on the page, counting from the top. Thus, if you desire to indicate the world “prisoner” and should find this word in the hundredth page of the book and the tenth from the top of the page, you would indicate it thus: [100]10. In this manner you can use a cipher without the possibility of its detection.¹

1. Official Records of the Union and Confederate Navies in the War of the Rebellion (Washington: Government Printing Office, 1883) series 1, volume 1, p. 762-763.