Radio Intelligence Service along Mexican Border
22 February 1918
When Major (later Major General) Ralph Van Deman finally succeeded in setting up the Military Intelligence Division, or MID, in 1917, he was particularly concerned about the country’s weakness in counterintelligence. He was convinced that German agents, spies, and sympathizers were actively operating inside America’s borders, a belief bolstered by the numerous attacks of sabotage, intercept of telegrams, and arrest of spies that had already occurred in the United States before war had even been declared on Germany. In addition, the new draft meant that the Army would be filled with citizens and aliens, and he feared enemy infiltration within the Army’s ranks.
MID attacked this threat with numerous weapons. One was a chain of radio Intercept stations along the US/Mexico border. The Signal Corps operated these Radio Intelligence Service, or RIS stations, as well as a number of mobile, truck-mounted systems, in order to monitor German diplomatic and agent activity during World War I.
The messages originated in Mexico and were transmitted either in Spanish or in code.
The activity was slow to produce usable intelligence because of the technical and security qualifications required of the operators. Nevertheless, the Radio Intelligence Service eventually had a number of intercept posts on the North American continent.
Mr. Richard Egolf was a member of the RIS in 1918, operating Tractor Units 33 and 34 in McAllen, Texas. He was interviewed by the National Security Agency’s History department in 1976, giving us a first-hand perspective of this early signals intelligence activity. When asked about the specific networks he targeted, he replied, “Chapultepec was the name of one of the stations that we monitored. Twenty-four hours a day because they were communicating with stations in Germany, and I presume with German submarines in the Gulf of Mexico.” Egolf recalled that the operators, who were on rotating shifts 24 hours a day, were told to monitor what time of day the signals were being transmitted, who was being called, and what the code was. The equipment was never shut off unless something went wrong and they had to fix it.
Radio intercept and direction-finding were new technologies in 1918. So were trucks. Putting the two together created capabilities that had never before been used by the Army. Mr. Egolf was asked how difficult it was to set up his mobile station:
“Well, the transmitting equipment had already been installed in the truck so the only setting up that the personnel had to do there in McAllen was to take the spikes out (which were the center of the umbrella antenna) and raise them and put the antenna up. The tent was set up right after the equipment came up there. We had a field meter which was hung on the wall, as well as an audibility meter. When you heard a station, you took readings on its signal strength and you came up with a pattern. You would then have a big lobe which was your strongest signal and then you took a reading – that was where the station’s signal was coming from. As you rotated the loop around in the opposite direction, the signal got weaker. You took this signal bearing and passed that information on to one of the other units.”
These early radio intercept sites gained information of great value from Mexico, Germany, and Japan. They also established to what extent Mexican government radio was being used in transmitting German messages back to Germany. The success of the Radio Intelligence Service in World War I helped to lay the foundation for the future use of radio intercept by the US military and this capability would become critical during the next world war.