“Hush … did you hear that?”
Josh froze in silence as he summoned the others in the room to do the same.
“I heard a truck stop right outside our door” he said in a low conspiratorial tone. They all knew the enemy Radio Direction Finding trucks were patrolling the area looking for allied spies and their French collaborators. The speed with which the RDF trucks could get a fix on illegal transmissions was alarming. As soon as the trucks had their fix a troop truck would be summoned, then it was game over in a hail of machine gun fire.
Josh had just parachuted in the night before and was sending his first message to confirm his arrival. An RCAF transport plane had dropped him right on target, behind enemy lines, in a small village in the south of France. He was met by French resistance fighters who hurriedly escorted him to a remote farmhouse off the beaten track secluded in a thick copse of mature oak trees.
In the early hours of the morning he had set up his simple wire antenna. It was a long random wire set into the trees. He had congratulated himself on how stealthy his antenna looked. Or perhaps, he thought to himself, since it couldn’t actually be seen from the road, his antenna didn’t “look” stealthy or otherwise.
The radio was standard allied forces issue, hand built by a team of dedicated technicians in England. It was a clever design that used the same tubes for multiple functions in the circuit. The antenna was directly connected to the set and roughly tuned by a variable capacitor. The plate current was adjusted to maximum by another control but, in those days nobody knew, or cared, about Standing Wave Ratio. There was no sidetone, so accurate sending using a straight key relied on the operator having a good fist and a keen sense of rhythym.
Josh had completed his rapid Morse Code training at a base in England. He had been recruited after showing aptitude for wireless telegraphy. Three weeks earlier he had been sitting in a waiting room at the recruiting office along with several other candidates. Josh knew his code but he was worried that his copying speed might not be fast enough. On a good day he could copy 20 words per minute, but the operational standard required was 25 words per minute.
From the next room he could hear Morse Code and listened to what was being sent. “If you can understand this message come right in.” While the other candidates looked vacantly around the room, Josh stood and walked confidently into the adjoining room and was recruited on the spot.
Now, here he was, sitting in the loft of a farmhouse in France with what the recruiters had told him was a life expectancy of just six weeks. The Germans were highly adept at catching allied spies and that made Josh very nervous. Very nervous indeed.
This time his fear was unfounded. The truck outside was not an RDF vehicle, it was a farm delivery truck. Next time he might not be so lucky. He turned his attention back to his radio. The output power was only 3 watts but he was receiving good signals from England confirming his transmissions were making it back to Blighty.
His task was to relay information about German troop movements using a fairly simple code in which short messages were sent in groups of 5 characters. Messages had to be short to avoid detection; 50 characters was the limit. At a Morse Code speed of 25 words per minute the message could be sent in just twenty four seconds. Linger on the air too long and the next sound heard could be the rattle of machine gun fire.
Here is how the code worked. The message to be sent was written in a single line with no punctuation or spaces. It was then divided into 5 groups of 10 characters and rewritten as a matrix with 5 rows and 10 columns. The first 5 character group to be sent was taken from the 10th column starting at the bottom. The second 5 character group was taken from the 9th column starting at the top. Each subsequent 5 character group started one column to the left, alternating in direction up and down the column.
The receiving station would use a form with 5 rows and 10 columns of empty boxes. The boxes would be filled with the character groups received starting with the 10th group which would be entered into the first column on the form, from top to bottom. The 9th group would be entered into the second column from bottom to top, and so on until all the boxes were filled. Once the boxes were filled the original decoded message could be read. Note that word spaces were omitted and had to be determined from context.
It was not a complex code so to create further difficulties for enemy interceptors, messages were never sent at the same time of day. Furthermore, an ingenious system of changing callsigns with every new message ensured further difficulty in identifying the sender. Every means of evading detection extended the life of the radio operator. The clever and the lucky made it past six weeks. Only a few survived the war.
Here is the first message Josh sent back from France to his unit’s base in England:
XAEAA BRWTA DNORN AUBOA NDUEI GTLNA CUCAR OMOOO ISIAE GYDNR
Can you decode it?