Life or death communications – the use of codes by Britain’s spies in the Second World War

Did you ever write messages in code when you were a child? I remember having fun believing that what I wrote to my friend was unreadable by anyone else – even though we only used a simple code where the letters of the alphabet were transposed a number of places. For instance, if we transposed the letters by two places we could send this message:

UJCNN YG IQ VQ VJG EKPGOC VQOQTTQY – I’m sure you’ll find it very easy to read!*

Communication is vital during war, particularly for agents who may be behind enemy lines, but sending messages can also be very dangerous. For agents of the Special Operations Executive (SOE) during the Second World War it was always possible that the enemy might decipher their messages or get a fix on the radio when the message was sent – both scenarios which could put the life of the agent in danger. To ensure a transmission was as safe as possible some sort of encryption was needed to keep the message secret.

Samuel Morse

Before learning how to encode a message the SOE agent would first have to learn how to send in Morse code which is a method of transmitting text as a series of ‘on’ and ‘off’ switches which are known as ‘dots’ and ‘dashes’ and are, in effect, a simple binary coding. The code is named after Samuel Morse who invented the telegraph in the 1830’s and needed a new electronic system to be able to send messages. Each letter or symbol in Morse code is represented by a series of these dots and dashes and it is the simplest and most versatile method of radio/telegraph communication. The most well-known grouping of letters in Morse code is the universal distress call    . . . _ _ _ . . . (dot dot dot dash dash dash dot dot dot), more commonly known as SOS.

But learning Morse code was only the first step for an agent who was preparing to go overseas as it was a universally known code and so the enemy would be able to read any messages that they sent. In the early days of the SOE agents used a simple, and consequently insecure, code known as ‘poem code’ to encrypt their messages. Both the agent and the person receiving the message would have a copy of the same poem. The sender would start his message with five letters to indicate which part of the poem his encryption would be based on; the message would then be written in columns before being transposed and transmitted. These poem codes worked well because they were quite secure but the agent didn’t need to carry a code book as they could memorise the poem. There were, however, weaknesses to this system. For instance, it was relatively easy to make a mistake when encoding; also, if the enemy managed to decode one message they then had all the information they needed to decode other transmissions from that agent in the future, and even ones they had intercepted in the past.

Leo Marks

The SOE knew that they needed to improve their communications system and so Leo Marks was appointed as codes officer. He found that the poems used for encryption had to be easy for agents to remember and so were often famous ones such as ‘Daffodils’ – the problem was that these famous poems would be known by the enemy and so make it easier for them to crack the codes. One of the first changes Marks made was to have original poems written for the agents to use rather than famous ones, these original poems were often comic, satirical or sexual to make them more memorable. Not all fell into these categories though, and one of the most famous of his original poems was, in fact, a love poem written for his girlfriend who had been killed in a plane crash; he later gave this poem to agent Violette Szabo to use when she was posted to France. (Violette was executed at Ravensbruck concentration camp in 1945 and her service in the SOE was commemorated in the 1958 film ‘Carve Her Name With Pride’).

The life that I have
Is all that I have
And the life that I have
Is yours.

The love that I have
Of the life that I have
Is yours and yours and yours.

A sleep I shall have
A rest I shall have
Yet death will be but a pause.

For the peace of my years
In the long green grass
Will be yours and yours and yours.

Violette Szabo

Another method Marks introduced was to simply use a different poem for each transmission to prevent any sort of pattern which might help the enemy. As it would have been hard for an agent to remember a number of poems correctly these were written on silk rather than memorised.

Leo Marks continued to work on more secure methods of encryption and the poem code was gradually replaced. The Worked-Out Key (WOK) system used a number of codes which were used only once and were written on silk (to be hidden in the agents clothing as described in my article on radio operators). Once a particular key had been used it would be torn off the silk and destroyed, leaving the next key ready for use. Marks went on to develop a One-Time Pad code where the letters of the alphabet were written in a list, the agent encoded his message by using a substitution square (i.e. substituting a different letter for each one in the alphabet). After being used once the list was thrown away and a different one used next time but still using the same substitution square. This was much safer than the poem code as there was no pattern to the listing of the letters of the alphabet and so even if the enemy managed to break the code for one message it wouldn’t help them with future ones. SOE agents liked this method as it was quick and secure.

As well as ensuring the safest possible codes Leo Marks worked on ways of deceiving the enemy through agent’s transmissions. One of these deceptions was Operation Gift-Horse which included key codes from the WOK system at the beginning of each message and fooled the enemy into thinking it was a poem code. The main aim of this operation was to get the Germans to waste their time trying to decipher coded poems when the message was, in fact, a completely different system. ‘Gift-Horse’ was used extensively just before D Day in 1944 at a time when there was already a huge increase in radio messages and so made the chances of the Germans decoding and compiling information about the invasion much more difficult.

So the types of puzzles which we find so enjoyable as a leisure activity had a far more serious role for a secret agent behind enemy lines. Maybe next time you do a puzzle in a magazine or a book you can take a moment to think of those for whom coding was not a simple pass-time but a key part of their work which, if not done correctly, could cost them their life.

*My code de-encrypted: SHALL WE GO TO THE CINEMA TOMORROW

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