Wilmingtonian Decodes German War Correspondence

Author: Jessica A. Bandel

Not every North Carolinian who served in the armed forces during the First World War carried a gun on the battlefields of France. Some, like Camelia Rutherford London, were administrators. Others served as nurses, artists, naval officers, and chaplains. In the course of my research, I’ve uncovered at least one person who served as a cryptographer—someone who specializes in encrypting and decrypting sensitive information—during the war period, Wilmington native Charles Jastrow Mendelsohn.

The only child of Rabbi Samuel Mendelsohn and his wife Esther Jastrow, Charles excelled in mathematics and foreign languages, obtaining a Ph.D. in classics from the University of Pennsylvania in 1904. He was employed as a professor of ancient languages at the City College of New York when the United States formally declared war on Germany in April 1917. As a civilian, Mendelsohn supported the war effort as a translator and interpreter of foreign languages for various government offices and as a censor of correspondence and newspapers with the postal service.

His expertise soon caught the attention of Herbert O. Yardley, an influential cryptologist of the time who recruited Charles to join the United States’ first cryptologic agency: Military Intelligence, Section 8, known more commonly by its abbreviated form, MI-8. In July 1918, Mendelsohn entered the army straight from civilian life with the rank of captain. The swearing-in ceremony was deeply moving for him: “[M]y heart is full to the brim of gratitude for the trust that America is placing in me, and the firm determination to serve her to the utmost limit of my slight powers—all to the end that peace may again spread her blessing among men, and that the world of the future may be a world without war and hatred….”

The entirety of his year-long military term was spent stateside at posts in Washington D.C. and New York City where Mendelsohn led a team tasked with decrypting intercepted German diplomatic correspondence. Using ciphers that had already been broken by the British, including one from the Zimmermann Telegram known as 13040, his team broke at least six of Germany’s diplomatic codes. Two of the deciphered messages shed light on Germany’s continued attempts to recruit support from Mexico. Though Mexico declined such offers, Mendelsohn’s work provided a deeper understanding of Germany’s interference with one of our nation’s neighbors.

In the eighteen months of MI-8’s existence, the group had deciphered and read over ten thousand messages and had broken at least 50 codes representing the governments of eight foreign nations. Despite its successes, the office was seen to have had little relevance after the Armistice. In the postwar years, the government drastically cut expenditures, reducing its own size and operations to that of the prewar period. MI-8 was shuttered.

Following his honorable discharge in August 1919, Mendelsohn returned to the City College of New York taking up a professorship in the history department. He continued cryptographic work on a part time basis, however, working for Yardley in MI-8’s civilian counterpart and precursor to the National Security Agency (NSA), the Cipher Bureau (known informally as the Black Chamber). The peacetime office was operated deep under cover, paying employees with cash from a secret payroll and fronting as the Commercial Code Company, a producer and publisher of codes used by commercial entities.

Through the publisher front, Yardley and Mendelsohn coauthored and distributed the Universal Trade Code, a commercial code used to save on telegram fees. The code worked by shortening phrases into words, reducing the overall length of a cable message. In an example provided by military intelligence historian David Kahn, “accounts subject to discount (of)” became “ACKWO,” which was far shorter and therefore cheaper to send than the full phrase. The publication was popular with businesses that relied on cable-based communication and sold well.

The greatest success for the government-side of the operation came during the Washington Naval Conference of 1921-1922, a convention of the world’s five largest naval powers—the United States, the United Kingdom, France, Italy and Japan—aimed at easing tensions in East Asia by curbing Japanese militarism and at preventing the possibility of another war through naval disarmament. During the course of the talks, the Cipher Bureau decrypted Japanese correspondence that betrayed the nation’s lowest agreeable terms. American representatives then used this information to push Japan to it.

Much to Yardley’s dismay, the Cipher Bureau was shut down by Secretary of State Henry Stimson in 1929, with Stimson famously remarking that “Gentlemen do not read each other’s mail.” The Bureau’s demise did not end Mendelsohn’s involvement in cryptology, however. Through close friend and fellow cryptographer William F. Friedman, he secured contracts for the composition of several pivotal cryptographic studies for the United States government. Among these were The Zimmermann Telegram of January 16, 1917 and its Cryptographic Background, which he coauthored with Friedman, and Studies in German Diplomatic Codes Employed During the World War. Both works remained classified for many decades.

Mendelsohn spent much of the 1930s conducting academic study of cryptology, composing several articles on the field’s evolution and history and building one of the best bibliographic collections in the world on the subject. David Kahn describes Mendelsohn’s myriad significant contributions to the field in no uncertain terms in his essay “Charles J. Mendelsohn and Why I Envy Him,” calling him the “first real scholar of the history of cryptology.”

In late 1938, as Germany’s international relations rapidly deteriorated and the threat of war loomed ever larger on the horizon, the U. S. Army’s Signal Intelligence Service reached out to Mendelsohn in the hopes of bringing him back as a cryptanalyst. Mendelsohn agreed, returning to service on a six-month contract in January 1939. He was paid via confidential voucher in order to keep his work secret, for “disclosure” of his name “in connection with this work would indicate the exact nature of the work.” Mendelsohn was in the process of renewing his contract when he contracted meningitis. On September 27, 1939, following five brief days of illness, he succumbed to the disease. He was 58.

Related Topics: