Some time ago I wrote a post on Ham Radio Outside The Box with the title “Six Weeks to Live“. It was a fictional story, based on historical fact, about the courageous members of the Allied Special Operations Executive working behind enemy lines on the European mainland during World War 2. Their task was to disrupt the enemy and relay intelligence by radio back to command centers in the United Kingdom. It was a dangerous mission, SOE operatives had a life expectancy of just 6 weeks before enemy RDF trucks located and terminated them.
I am fascinated with the radio technology of the era and have read several books on the subject. During my childhood I began my radio hobby using military surplus components with which I built crystal sets and a regenerative receiver (that turned into an accidental broadband transmitter, as regenerative sets are wont to do).
Then, earlier this year, I learned about a new group of CW enthusiasts being formed by Drew Kowal AF2Z. It is called RandomGram. Each month RandomGram members exchange 5-letter code groups to practice accurate sending and copying. Of course, I was immediately interested. Here was a chance to practice my Morse Code while fantasizing about how it must have felt for those brave SOE operatives during WW2 whose very lives depended on transmitting quickly and accurately using secret radio equipment and stealthy antennas.
I should stress that, to the best of my knowledge, there is absolutely no hidden code involved in RandomGram’s 5-letter groups. I kind of wish there was actually. It would be added fun to be able to decode secret messages from the code groups received. Hams are forbidden from sending encrypted traffic, which is a shame, but perhaps if the encryption technique was very simple and published for all to understand …?
Here is an extract from the story Six Weeks to Live that describes the actual simple encryption code used during WW2.
… 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.
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