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Tactical Signals Intelligence Originates in World War I

Published with Permission by:
Lori S. Tagg, Command Historian,
US Army Intelligence Center of Excellence, Fort Huachuca, AZ.

After the invention of the radio in the 1890s, the first widespread use of the technology for military communications occurred during World War I.  The ease of intercepting radio messages quickly spurred advances in encryption and decryption of codes and ciphers.  The Military Intelligence Division in Washington recognized the importance of this discipline and quickly established Herbert Yardley’s Code and Cipher Section.  Likewise, shortly after arriving in France, Brig. Gen. Dennis Nolan, the American Expeditionary Forces (AEF) G-2, was forced to acknowledge that the US was woefully unprepared to exploit signals intelligence.  When British intelligence informed him that it had identified two-thirds of the enemy’s divisions through the intercepting and decoding of Germany’s radio messages, Nolan acted immediately.  On July 28, 1917, he tasked Capt. Frank Moorman to form the AEF’s Radio Intelligence Section (RIS), also known as G-2 A6.

Moorman, a 40-year-old Coastal Artillery officer serving as the acting director of the Signal School at Fort Leavenworth, had served in the Military Information Division in the Philippines and had temporarily worked with Parker Hitt, the Army’s foremost authority on codes and ciphers.  When Moorman arrived in France, however, he understood little more than his mission: to read and decipher German radio messages.  Starting from scratch, Moorman soon built a successful collaborative network that provided the AEF with reliable intelligence throughout the war.

Lt. Col. Frank Moorman and his staff of the Radio Intelligence Section, AEF Headquarters (INSCOM photo)

The US Army’s Signal Corps, which had responsibility for Army code compilation and communications security, figured prominently in Moorman’s network.  The Signal Corps’ own Radio Intelligence Service, later renamed the Radio Section, established, operated, and maintained listening stations close to the front lines.  Personnel manning these stations intercepted and copied enemy radio messages around the clock.  The Signal Corps turned recorded messages over to RIS personnel at each Army headquarters for deciphering and analysis using keys provided by the G-2 A6. The most difficult codes and ciphers and potentially important messages were passed further up the chain to Moorman’s section.

The US Army’s first foray into tactical signals intelligence quickly surpassed the efforts of its Allies.  Its eight listening stations intercepted more than 72,000 messages and 238,000 telephone calls.  Additionally, personnel located enemy radio stations, constructed net diagrams, intercepted and located radio signals from airplanes ranging for hostile artillery, policed US Army telephone lines near the front for operational security, and distributed American trench codes.  They also helped develop enemy order of battle through traffic analysis by using call signs and knowledge of German communication protocols.

One early success occurred in December 1917, when the RIS intercepted a transmission indicating the enemy planned a barrage in an area where a US division was co-located with the French.  The RIS passed this intelligence to front line headquarters just in time to allow the Allies to unleash a counter-battery attack that effectively prevented the Germans from carrying out their plan.  Examples like this quickly won over skeptical commanders who initially distrusted the value of code and cipher work. However, it also exposed a vulnerability for future warfare. Moorman cautioned that the system developed for use in World War I was successful primarily because of the static nature of trench warfare.  Its value decreased when the enemy became mobile and the RIS could not maintain close contact long enough to establish the listening stations and install the necessary equipment.

In 1920, Moorman spoke to the officers of the Military Intelligence Division in an effort to pass on insights relevant for the future.  He recalled that his most pressing problem was obtaining adequate personnel: “The difficulty in finding men who could actually think without a guardian was surprising.  It is hoped that one of the aims of the future will be to develop this ability in men chosen for code and cipher work.”

Another obstacle the RIS faced was educating outside personnel about the process of code and cipher work.  “What [headquarters] wanted us to do was pick out the important messages, decode them, and let the rest go.…It was a matter of considerable difficulty to make them see that we had to work them out and that the Germans did not tag their important messages before sending them.”  Additionally, educating troops about the importance of safeguarding their own communications was paramount.  Moorman warned, “It is a sacrifice of American lives to unnecessarily assist the enemy in the solution of our code.”  Too often, soldiers mishandled codes and refused to “[observe] the ‘foolish’ little details that the code man insists on.”  Moorman correctly predicted that all these issues would endure in the future.