Codebreaking During Prohibition

May, 2017

The Caesar cipher, is the earliest known record of a system created for secret communication. Devised by Julius Caesar, it was used to transmit military commands that would appear scrambled if intercepted by their enemy.  By agreeing to a shifting system, the sender and receiver would be able to replace each letter and create or unravel the secret message.  This shifting cipher system was so successful that it continued to be used by military leaders hundreds of years after Caesar. That is, until it was decoded 800 years later by Al-Kindi an Arab mathematician who discovered a vulnerability by counting the frequency of each letter and discovering a consistent pattern.  This led to the knowledge that each system of communication has a fingerprint based on the frequency on which the letters are used, and this became the most valuable tool for a code-breaker.  

While the business of hiding and decoding messages has a long history in military strategy, it was also used in commercial spaces for those trying to transport contraband items by eluding the law.  Hence, it’s not surprising that Elizabeth Smith Friedman, a language and English major who developed an interest in ciphers became the first female cryptanalyst employed by the Coast Guard to break codes sent by rumrunners.  Edward Behr points out the crucial role she played in prohibition when he states that “largely at her insistence, the Coast Guard eventually launched the CG-210, a patrol boat packed with high-frequency receivers and direction finds, and staffed with trained cryptanalysts that could listen in on a large number of coded messages simultaneously.” (Prohibition: 1996) 

Elizabeth Smith Friedman - US cryptanalyst

Elizabeth Smith Friedman - Chief Cryptologist for the U.S. Treasury Department

During Prohibition, and in her role as code-breaker for the Coast Guard, she would go on to testify in many court cases. In 1933, Ms. Friedman, in her capacity as the chief cryptologist for the U.S. Treasury Department, was “called as an expert witness in the criminal trial of master international rum-runner Bert Morrison in New Orleans” (The Mob Museum). In a New Orleans courtroom she provided testimony against Bert Morrison and his employer Consolidated Exporters’ Company and gave this example of encoded instructions:

“Anchored in harbor. Where and when are you sending fuel?”



For her groundbreaking vision she received praise and media exposure and went on to establish and head a new cryptologist unit where she trained and mentored others.  Her work highlighted her belief that “young people with the proper qualifications should be trained in this mental battle against the underworld of smuggling.” Ms. Friedman’s work was groundbreaking and although she admitted that it made little impact in curbing rum-running activities, her work and her team were successful at intercepting other commercial smuggling activities and diplomatic endeavors.  Her intelligence in code-breaking was undeniable and David Kahn the author of Code Breakers believes that “without prior work on bootleggers’ code-breaking, progress in WWII cryptanalysis against Germany and Japan would have been far less successful.” (Prohibition, 1996 - Edward Behr)

Today too, the battle continues, with the fight for cyber security becoming an indomitable part of our political and commercial lives.  To learn more about Ancient and Modern Cryptography check out the free course on Khan Academy


Marshall Foundation

The Mob Museum

Khan Academy

Behr, Edward. Prohibition: 1996


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