Radio Kills: Rommel’s 621st Radio Intercept Company
You know life is rough when you welcome British food. But Captain Alfred Seebohm, commander of the German Afrika Korps’ 621st Radio Intercept Company, traded for cans of bully beef whenever he could. His focus in life was British military radio traffic, so why not eat their food, too? Seebohm’s 621st was a set of ears for his commander, Lieutenant General (later Field Marshal) Erwin Rommel.
Rommel needed to know who he was fighting, where they were, what they were planning to do, when they would do it, and how they would do so. Not surprisingly, his British-led opponents did not want him to know any of these things. He needed intelligence—men from different disciplines trying to learn who, where, what, when, and how.
- Subscribe to Armchair General Magazine
- Subscribe online and save nearly 40%!
Seebohm was not Rommel’s only ears. The German Cipher Branch could read the U.S. State Department’s Black Code. Cipher Branch decrypted the reports of the U.S. military attaché in Cairo detailing the British situation in North Africa and shared them with Rommel.
But hearing is an imperfect sense and does not provide as accurate a picture as a combination of the senses does. It is harder to deceive all the senses than to fake out just one. So it is best to think of the 621st as very good ears and nothing more.
This is not an attempt to downplay the unit’s successes; rather, it is simply putting them in context. Too often there is a tendency to attribute success in intelligence to a single source. That can be true, but it is not for the 621st.
The 621st sometimes provided some excellent intelligence all on its own. But many of the unit’s successes are better described as successes of German intelligence combined efforts in which the various senses worked together, fusing their outputs to give a much better picture than any one of them could individually.
* * *
The intercept truck landed on the dock at Tripoli with a thud. Lieutenant Gerisch mouthed a curse. The ship carrying the advance radio intercept platoon "Afrika" had just run the gauntlet of British attacks between Italy and Libya. Gerisch had not survived that only to lose the equipment to some clumsy crane operator. After a few choice words from Gerisch, the operator was much more careful. March 1941 found Gerisch’s platoon deployed at Sirte, Libya.
Seebohm docked on April 24th with another radio intercept platoon, a radio direction finding platoon, and Lt. Wischmann’s group of cipher specialists. All 300+ men of the company linked up in Sirte.
The unit’s nomenclature initially was 3rd Company attached to the 56th Signals Battalion. (It did not become the 621st until April 1942, in a move aimed at deceiving the British.)
North Africa was an intercept-operator’s dream. The campaign’s mobility and fluidity necessitated widespread radio use. But this was an entirely different theater of war for Seebohm’s men. Sand flies drove everyone crazy and could cause infections. Many men got sick from their salty drinking water. There were sandstorms and relentless heat.
Operational challenges abounded. The 621st could not intercept or carry out direction-finding if its platoons were on the move. Yet, they had to be on the move at some point in a campaign in which the front line was always changing—often changing rapidly. Seebohm had to balance out positions that could intercept communications, would allow communications with the evaluation center, and were safe for what was a support, not a combat, unit. Seebohm did his best in juggling these competing demands.
Communications occurred on the HF bands primarily in Morse code. Seebohm started out by having his operators scan the bands for unencrypted English traffic. It might be enciphered.
A radio network typically has a control station and a number of out stations. All traffic goes through control and the out stations generally do not contact each other directly. Each station has a call sign, usually a code word. For instance, the coded call sign for the British 8th Army at one point was "MXQ."
As the intercept operators found the various British radio nets, they had to determine what radio network they were listening to and its purpose. The British made their job much easier in mid-1941 through lax communications security. They did not always use codewords. So a British radio operator might try and contact "8th Army" instead of MXQ. Now the Germans knew what MXQ was. The British compounded the problem by not changing the various code words very often.
There was also too much chatter on the British radio nets—gossiping really—and no real radio discipline. Another bad British habit was too much "cc’ing" of messages instead of simply leaving these addresses off of messages that did not directly concern them. From just one message, Seebohm could learn all the out stations (subordinate units) to the control station (commanding unit). He could combine that with a captured codebook and/or good traffic analysis, and a British order of battle could be built up over time.
Each Morse operator has a "fist" as unique as his voice. Seebohm’s intercept operators learned to recognize the British radiomen. The British typically failed to move their radio operators around, so each unit had a unique identifier. It did not matter if the unit’s coded call sign changed; the fist allowed the two to be linked.
The intercept operators passed along what they heard to the company’s evaluation center. German patience and thoroughness combined with British laxity and mistakes allowed the company to start to assemble the puzzle of who they were hearing. The traffic analysts began to create a British order of battle.
Lieutenant Wischmann’s team of cipher specialists now came into play to figure out what they were hearing. His team was co-located with the evaluation center. German radio intercept companies typically did not have such specialists attached to them. But the Africa Corps was so far from higher echelon intelligence centers that an exception was made to facilitate the decoding of British traffic.
Where the British units were was the job of the direction-finding platoon. The platoon’s elements set up close to the front lines and passed their results to the evaluation center. The evaluation center then combined the results to determine the rough location of the intercepted call signs.
What Seebohm really wanted was the British headquarters nets at the brigade level and higher. He got them. The intercept operators continuously monitored the frequencies of these nets, copying and passing along all traffic on them. The direction finders did their part by making sure that the stations in these nets were still in the same locations as previously determined.
Seebohm created a radio situation report from the various inputs of the company. He issued his first report on May 2nd. But the best reports in the world are meaningless if they are too late. Rommel was always on the move, so Seebohm attached a small liaison team that traveled with him and was in constant communications with him. Seebohm also took steps to ensure that his units were in good communications with one another.
Seebohm’s first success was in mid-May when the 621st correctly evaluated British movement as offensive, allowing Rommel to quickly respond. They had not predicted the offensive, but they did take note of the various indicators that had occurred before it, especially the use of a single codeword sent to all units.
The direction-finding platoon detected a shift of British armor on the Sollum front in early June and correctly deduced that another offensive was in the making. On the evening of June 14th, the use of a single codeword was heard again. Seebohm informed Rommel that a British offensive was imminent and Rommel immediately shifted his forces. The British BATTLEAXE offensive started the next day. The German unit intercepted a lot of significant traffic in the clear during the battle, including British commanders debating what to do and units complaining about the lack of ammunition.
The capture of a British code book early in the battle also helped the 621st, giving them a much better understanding of what they were hearing—including a message that indicated the British now intended to retreat.
The British then tightened up some of their radio procedures. It worked. Radio silence allowed the British 7th Armoured Division to withdraw undetected. The 11th Hussars and the 4th South African Armoured Car Regiment switched radio operators, a move that deceived the 621st as to which unit they were hearing.
Radio intercepts weren’t the only source of information; successes did come by close cooperation with other intelligence means. A reconnaissance regiment was detected by the 621st and their position was then confirmed by German air reconnaissance. The same procedure confirmed the location of the 1st South African Division in early November 1941.
British communications security was better for their November CRUSADER offensive, and their units got into their assembly areas undetected by the 621st. A captured code list once again aided the unit during a British offensive. Seebohm learned that the 5th South African Brigade had been destroyed, as repeated calls to it were not answered.
The offensive lasted long enough for the 621st to once again compile an Allied order of battle. Seebohm noted the 70th British Infantry Division was newly deployed at Tobruk. His direction-finding platoon detected the British withdrawal as the locations of the various divisional headquarters shifted to the rear.
In January 1942 the 621st learned that the 2nd New Zealand Division was leaving due to a careless message in which they said goodbye and wished the other units well. They had been mauled in CRUSADER and were withdrawing to Syria. Seebohm learned of the British retreat on January 24th.
The 621st detected units of the 1st Free French Division in late January. Direction finding was also quite active, placing the 11th Indian Brigade at Maraua, the 1st South African Division at Bardia, and the 1st Armoured Division at Mechili.
The British further tightened up their radio security in April and changed codewords much more often.
A German platoon detached at Tobruk achieved success in May when a decoded message told of the breakout routes that an Allied unit was going to use. That unit suffered heavy losses when it tried to do so.
The intercept platoon rejoined in late June. Seebohm positioned both intercept platoons barely a half mile behind the front line at a place called Tel el Eisa. The site was on high ground, great for intercepting and for communicating with the evaluation center and the liaison team with Rommel.
The British took notice of the unit, with air reconnaissance flying over its position. They also intercepted and decrypted the Enigma traffic between the unit and the evaluation center. The British became aware of the company’s mission and planned a raid.
Australian troops led the raid on the night of July 10th. Italian troops co-located with the intercept platoons fled. Seebohm happened to be visiting the platoons at the time. Both he and his unit fought as best as they could, but rifles and machine guns were no match for tanks.
Seebohm was wounded and died soon after. Seventy-three men of the intercept platoons were captured, along with their equipment and a treasure trove of documents detailing what the unit had done.
So why didn’t they flee? Seebohm had been dressed down by a colonel when the unit had previously pulled out of a position. The colonel did not know the unit’s mission, but Seebohm vowed that it would not happen again. Any really safe position would not have been as effective an intercept position, either. Rommel was furious that the unit had been wiped out.
The loss decimated the 621st. The equipment and men were replaced, but they simply were not as experienced as the original intercept crews. Equally important, the British were completely aware of their vulnerabilities and made further radio security changes. They started with a week’s radio silence.
The 621st intercept company had a good run, particularly in conjunction with other German intelligence branches, but that run was now over.
About the Author
Hans Johnson is a freelance writer who lives in Florida.