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SIGINT OPERATIONS IN THE EUROPEAN THEATER DURING WW2

Editors note: The following article was derived from the history project of the 118th Signal Radio Intelligence Company (SRIC) published by John W. De Grote. Mr. De Grote, who was an Intercept Operator with this unit, has been kind enough to allow us to edit this information in order to show how these units operated and afford you a chance to compare this with how others may have operated in the future.

During WW2 SRICs were attached to the various US Armies whereas Signal Service Companies (SSCs) were attached to various Corps within the Armies. SRICs were manned at a level twice as large as a SSC. Additionally, the SRICs utilized 3 DFs whereas the SSCs usually had 2.

The 118th SRIC was activated on May 9, 1942 at Camp Forrest, Tullahoma, TN. They arrived in Great Britain on January 29, 1944 and landed on Utah Beach on July 15, 1944. Primarily supporting Gen. Patton and the Third Army, they followed the action until the end of the war. Following the surrender of Germany, the 118th was stationed in Rosenheim (Bavaria) until their move to Zipf, Austria, on August 18, 1945. It was there on April 10, 1946 that the unit was deactivated.

Prologue: The movement of a SRIC involved some fifty vehicles. Heading the column would be Jeeps, 3/4 ton weapons carriers and 2-1/2 ton GMCs carrying kitchen equipment, headquarters and supply. These were followed by eight 2-1/2 ton GMCs of the Intercept Platoon, three of which pulled PE-95 power supply trailers. Then three Chevrolet semi-trailer vans plus 1 deuce-and-a-half with a PE-95 for the Intelligence Platoon and 1 deuce-and-a-half for DF Control. A detail of some 30 men was sent in advance of the main convoy to scout the new area, decide where the various platoons were to park and assist in the parking. This system allowed the unit to become operational within the shortest possible time.

THE INTERCEPT PLATOON: This platoon was made up of four sections of 25 men each, plus the platoon officer and platoon sergeant. Full strength was never fully attained and the sections normally averaged 22-23 men. The platoon had eight 2-1/2 ton trucks, 2 for each section, and each was fitted with a hutch. One truck of each section had a small switchboard and 4 intercept receivers while the other truck had 5 intercept receivers and a telephone connected to the switchboard of the first truck. Equipment was mounted to the right of the hutch door. The switchboard of each section was connected to the Traffic Analysis (T/A) section of the Intelligence Platoon and to DF Control.

Each section had a PE-95 power generator. The PE-95 had a 6 cylinder GMC gasoline engine that drove a 115 volt generator and the entire assembly was mounted on a heavy 2 wheel trailer. Only two generators were used at any one time, the other two being held in reserve. Each section sergeant appointed one of his T/4's to act as crew chief and operate the switchboard. It was also the T/4's duty to keep the generators running. This meant checking the oil, and refueling the gas tanks when necessary. This job was given to the crew chief because the intercept operators did not leave their radios except for a call of nature.

The sections worked three eight hour shifts. During daylight hours each section worked a full crew of 10 men, 9 on radios and the crew chief on the switchboard. This meant that there were 36 intercept positions operating on the first shift. The second shift generally used somewhat fewer operators, while a skeleton crew, using only the switchboard hutch, manned the third shift. The most powerful radio receivers in existence at that time were used to intercept the German transmissions. They were the 22 tube RCA, the 24 tube Hammarlund Super-Pro, and SCR-178s which were Army Signal Corps radios built by Hallicrafters.

The most desired enemy transmissions were from Panzer Divisions, messages sent from tank to tank, and tank to command post. However, all signals were assumed to be of importance by the intercept operator. The strength of all signals were kept purposefully weak by the Germans in an attempt to avoid interception. They used radio frequencies between 600 and 1600 kilocycles (long wave) for most of their transmissions. At these lower frequencies the signals had more power along the ground (ground waves) to overcome hilly terrain and other obstacles. Short wave frequencies were also used, especially by the higher powered stationery transmitters but these signals were less desirable because they used codes with "pre-fixes" that were virtually impossible to break.

Coming into a new area, the intercept trucks were lined up side by side, usually against a hedgerow or under a row of trees, so they could be more easily camouflaged. Trees were also used in erecting the wire antennas. Various types of antennas were used, from whip antennas to L-type which consisted of wires strung from the intercept hutch to existing trees. For the whip antennas, a mount was driven into the ground and then the antenna placed in the mount. The PE-95s were parked in front of or between the trucks to keep the necessary cables as short as possible.

While the Intercept Platoon was usually in operation within 20 to 30 minutes after arrival, the dreaded job of camouflaging all units took somewhat longer. Dreaded because the nets were so large and heavy, plus they caught on every part of the equipment as they were being pulled over the high trucks.

THE INTELLIGENCE PLATOON: When arriving at a new area the three semi-vans were parked in the location selected by the platoon officer, which was usually near the Intercept trucks. Because it was necessary for men of the platoon to go from one van to another quite often, they were parked in a "Y" formation with the doors at the end of each van in such close proximity that a plank could be placed from one door to another. This set-up allowed movement between the vans without climbing up and down steps. The platoon was divided into three main operating sections: Traffic Analysis, Cryptanalysis, and Order of Battle.

Traffic Analysis (T/A) Section - This section studied the make-up of German Army radio networks. This furnished useful information about the units themselves, such as which was "control", presumably headquarter; and where the sending units were located, aided here by data furnished by the Direction Finders. Since German "nets" changed call signs and frequencies daily, T/A's job was to determine if these were the same stations previously copied. They were aided by the intercept operators who could often recognize the "fist" of the German operator. T/A was also aided by captured German documents which showed the method by which call signs and frequencies were changed. It was also in direct phone contact with the switchboards of the Intercept Platoon and DF Control.

Cryptanalysis Section - This was the code breaking section. Their purpose was to glean any possible radio intelligence from German messages that had been copied by the intercept operators.

The cryptanalysts worked virtually exclusively on messages sent using "three letter" (T/L) code groups. These messages were encoded in the German field code know as HST which stood for Heeressignaltafel, literally "Army Signal Table". The HST (T/L) code was used by all German Panzer units, as well as others, for communications at division level and below. The basic HST code had about 500 code groups, with a list of meanings, called "idents", which varied according to the nature of the unit. Thus, idents for a Panzer unit would differ from that of an Infantry unit.

The T/L code was designed for tactical purposes - the immediate necessities of the battlefield. As such, it had to be easy to use and be sufficiently secure to defeat successful analysis for a limited period of time. There were a very considerable number of possible combinations of 500 code groups so they could be reshuffled every 24 hours on a pre-determined basis. This was accomplished through distributing a 30 day supply of code lists in advance. It was a good system for the purpose for which it was intended - to provide field units with a simple, easy-to-use code for transmission of tactical day-to-day information.

A portion of these 500 code groups were allocated to the alphabet and numbers so that place names and geographic references could be spelled out, eliminating the need to use up code groups which could not have been predicted in advance anyway. The cryptanalysts sought to read enemy traffic by analyzing the messages for patterns, such as repetitions of certain code groups. If they suspected a message contained use of a "speller", this provided a point of entry in attacking the message. Again, other information, such as DF "fixes", would be helpful here. Another section of the HST (T/L) code was what cryptanalysts called "semi self-evident", because the three letter groups were virtually abbreviations or acronyms for German words. For example, AFZ was aufschlagzuender, meaning "contact fuse", an artillery term.

The Germans also used 5 letter code groups for messages sent by higher echelon units. The cryptanalysts occasionally worked on this type of traffic that was called "N/I" (non-indicator), but were less successful. These types of messages, which were probably encoded with the German "Enigma" cipher machine, were routinely sent on to higher headquarters, probably G-2 of the Army Group.

Order of Battle Section - Essentially the job of this section was a sort of research function, collecting and storing information about the German military forces from all possible sources. This data could be useful to both the T/A and cryptanalysts at some future time. Further explanation of the functions of this section will be found in the "Operations" section following.

DIRECTION FINDING PLATOON: The platoon used three DF units which were identified as Able, Baker and Charlie. The DF Control unit was located in the main Company area. Since the DF units were set up away from the main Company area - usually from ten to twenty miles apart - it was not feasible for them to move with the main Company convoy. Rather, they each moved individually to their next location which, in all cases, was closer to the "front" than the Company area. The officer in charge of the platoon picked the sites. The sergeant in charge of each DF unit was given maps and the coordinates for the new location. On one such move Baker DF was given a location that had not been cleared by the infantry and had to wait until given the OK to set up their unit.

Arriving at the new location it usually took from 45 minutes to one hour to set up for operations. This consisted of assembly, placing the antenna, then leveling and orienting the structure to magnetic north. Later, when the Company began to make more frequent moves, the DF units were mounted on 3/4 ton trucks so that all that had to be done in preparing to move was to remove the antenna and camouflage and drive to the next location. When setting up again it was just necessary to orient, level the truck, reinstall the dipole antenna and camouflage. Each DF unit consisted of nine men and a truck driver. The DF units were small and could only accommodate one operator on duty at one time. The shifts were generally two hours in length with one man on guard duty who also worked a two hour shift. The DF units usually operated only in the daylight hours except in periods of high German radio activity. On night time guard duty, two men worked a shift of four hours.

The DF unit hutch contained a radio receiver, a frequency meter, telephone and a wheel to turn the highly directional dipole antenna mounted atop the hutch. The units were always placed on the highest ground in their designated set-up area and away from all trees or buildings. The DF units were disassembled and placed into their cases when moving. The case was a large green box, about the size of a coffin. When arriving at a new location they were removed and completely reassembled. After arriving at a new location, and completing their set-up, it was necessary for the Wire Platoon to lay wire back to DF Control, in the main Company area, as they could not become operational until they had phone service.

WIRE PLATOON: The main purpose of the wire platoon was to furnish telephone service to and between all segments of the Company. Phone service was vital - without it the Radio Intelligence Company could not function. The platoon was made up of 3 wire crews and 3 T&T (telephone and teletype) crews. Each wire crew was made up of nine men.

When the Company began a move, each wire crew was assigned to a DF unit, and in many cases traveled with their assigned DF unit to the new location so they could begin laying wire back to the Company area. This was usually started even before the DF unit was assembled. Wire was laid along roads, in ditches, or sometimes on existing telephone poles. While wire was being strung for the DFs, other men of the wire teams laid wire between the Intercept switchboards to the Intelligence Platoon vans and DF control. Phone service was also established for Company headquarters. Another job of the wire crews was to the stringing of wire from the T&T van to "Lucky Forward" [Gen. Patton's Headquarters], for the purpose of establishing teletype communications.

The T&T crews worked three shifts of eight hours each. They operated the teletype service to Third Army head-quarters and also the main Company switchboard, both located in the hutch of the HQ unit. They were in continuous operation and never closed. Teletype communications were very effective and reliable. Since their circuits could not be tapped into, without causing the machine to shut down, they were used extensively for sending secretmessages. The operators handled large volumes of traffic, many messages being sent and received each day. The system worked very well for that era.

OPERATIONS OF THE SRIC: Operations were basically controlled from the vans of the Intelligence Platoon. As the Company began operations in the new area, intercept operators would start searching for German radio signals as soon as set-up was concluded. The 118th had some of the best operators in the world. From practice in England they had become so adept that they could tell by the sound of the Morse code being intercepted if it was a German operator, plus the actual tone of the German transmitters was an aid in this endeavor. As soon as operators located and copied messages, they would be picked up by a courier from the T/A Section.

At this point, the T/A Section would take over the intelligence gathering procedure of the Company. Messages were analyzed and instructions sent by telephone back to the crew chief at intercept central to keep on copying that frequency or to resume searching. If T/A believed that valuable information could be gained from the messages being copied, then it would be of extreme importance to determine the location of the sending transmitter. The Company Direction Finding units would now be activated in much of the following manner.

The T/A Section would inform the operator at DF Control as to the call signs and frequency of the desired station(s). In turn, DF Control would contact each of the DF sites, passing on this information and request a "fix". Once the DF site had picked up the desired signal they would rotate their directional dipole until the "fix" was obtained. The coordinates (in degrees) of this "fix" would be telephoned back to DF Control who, in turn, would relay these findings to the Order of Battle section. If transmissions were sparse the DF operator would have to "sit" on the frequency and wait for transmission to resume. To be sure of the exact frequency, Frequency Meters were used. These little frequency meters were absolutely accurate and when used made it possible for all three DF sites to obtain "fixes" simultaneously. The trick chief at intercept could "zero in" on the frequency of the receiving intercept radio and then this precise frequency would be relayed to the DF sites. It then took the DF operators a matter of seconds to zero beat their receivers to the desired frequency and "fix" the transmitters when they came up again. At times, when different transmitters were separated by some distance, it was possible to obtain "fixes" on several stations operating on that frequency.

The Order of Battle section would plot these "fixes" on an acetate that covered a map of the sector. This map would cover the wall of operations and was copied from a photograph of the map that was kept in the Gen. Eisenhower's headquarters. Copies of the master map were received daily by courier. Using a wax pencil, the acetate would be constructed showing the present front, location of know Germany units and the location of the transmitters plotted from the DF fixes.

It was desirable to keep six or eight operators searching at all time since it was possible for a German network, previously not heard, to become active at any time. If some dials were not moving these transmissions would be missed and any possible intelligence lost. Also, if a previously active network became silent for an hour or two, the intercept operator may have been told to resume searching but to return to that frequency every fifteen minutes to check for a possible resumption of transmissions. All intercept operators turned in a log at the end of each shift stating the frequencies copied, call signs of the networks, time spent in searching, etc.

From this description of "operations" it is hoped that the reader has been given a picture as to how the various platoons worked together to reach the desired goal of gathering and supplying useful radio intelligence to Third Army headquarters and beyond

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