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“The people of the United States themselves were allowed to know nothing of the communications between Pershing and the War Department. The successes or failures of the American Army depended on the safeguarding of secret reports and instructions. If the enemy was able to intercept and read these messages, the most intricate stratagems of the Americans were futile.” (Herbert O. Yardley in, The American Black Chamber, p.39)

The American Patriot: The Start of Everything

Prior to June 1917, the Government had no existing department that conducted cryptanalytic activities. However from June 1916 to about December 1920, a considerable amount of such work was conducted, as a patriotic enterprise, by a new Military Intelligence division called, MI-8. MI-8 was the first cryptographic bureau to exist in the United States, and among the leaders of this department was Herbert O. Yardley. Although it was first located on the balcony of the War College Library, the department’s rapid growth instigated its relocation to the top floor of a house on F street in downtown Washington, D.C. 

Code & Cipher Solution

The code and cipher solution subsection was what would now be called the cryptanalytic subsection. It was the largest of the subsections of MI-8 and performed the cryptanalytic work not only for the War Department but also for all other Government departments, including Navy, State, Justice, and the two censorships—Cable and Postal, which were then separate organizations.

Code & Cipher Compilation

This section was primarily was primarily formed when the Signal Corps received Germans codes from the War Department Telegraph Code. After receiving such documents, MI-8 found it necessary to establish this section. This section produced several codes such as Military Intelligence Code No. 5 and No. 9, small pocket codes for secret agents, and the like. 


MI-8 trained the majority of the personnel sent overseas for cryptanalytic duties with field forces, both AEF and Siberia. (It must be mentioned, however, approximately 85 officers were trained at Riverbank Laboratories, where a six-week training course in cryptanalysis was given these officers prior to their shipment overseas.)

Secret Inks

The section developed invisible inks for their agents, examined letters for secret writing, and examined over 2,000 letters a week for the military and postal censorships from 1 July 1918 to 1 February 1919. 


Main purpose of this subsection was to handle messages to and from military attachés and intelligence officers that served abroad. Approximately 25,000 messages were sent and received in a nine months period, practically all in code

Shorthand & Miscellaneous

Handled captured documents and texts in many shorthand systems, such as in German, which often had to be deciphered.  This was the first subsection MI-8 organized, when censorship began sending (October 1917) letters and documents supposed to be in cipher, but that was actually in shorthand. The subsection provided trained linguistics for MI-8 and the AEF.


  • With his new leadership position and his new title of Second Lieutenant, Yardley set out to uncover more eager American cryptographers like him, stationed all over the world. Out of his numerous calls, the first Captain to arrive was Dr. John Manly, the head of the English Department at the University of Chicago.  Upon their first meeting, Yardley describes the 52 year old philologist as,"…a small quiet-spoken scholar…Captain Manly had a rare gift of originality of mind—in cryptography called ‘cipher brains.’ He was destined to develop into the most skillful and brilliant of all our cryptographers. It is to Captain Manly that I owe a great measure of the success achieved as head of the War Department Cipher Bureau."(American Black Chamber, Page 39


    ​ Soon after Dr. John Manly's hire​, MI-8 was efficiently working and its growing success allowed for the hire of ten more clerks. MI-8's continuous growing success coincided with that of that of the American troops in the war.

Despite minor setbacks throughout the war, MI-8 's, and most specifically, the code and cipher compilation subsection, involvement saved thousands of American lives from the start of their involvement, in 1918 until the end of the war.

By January 1918, MI-8 had gained so much success that the Code and Cipher Solution Subsection had immensely grown. The subsection was now training students for their own use, but also the recruits for General Pershing’s Cryptographic Bureau in France.


Cipher Brain

General Pershing

Clarified terms
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