and will insert the prefix for that particular panzer division, say COD, then type the message on the Enigma machine in the appropriate Wehrmachit cipher, take the scrambled (and thus enciphered) result, and transmit it on that panzer wireless frequency.
‘Out in the Western Desert, wireless operator Schmidt listening on his frequency hears the letters COD in Morse, recognizes it as the call sign of the 15th Panzer division and copies down the Morse signal. It is, of course, the letters COD followed by what seems to be gibberish.
‘That signal is then taken to the 15th Panzer division’s Enigma. Right at the beginning of the message, following COD, is another three-letter group which tells what the machine should be set at, and, if it is very secret, an indication that it must be deciphered by an officer. I’ll show you all that on the machine in a moment.’
‘As easy as that, eh?’ Jemmy grunted.
‘If you have an Enigma, and if you have the appropriate manual for the cipher being used and can set the machine correctly. For the eavesdropper — us, in fact, — it’s more complex. We can usually work out for whom the signal is intended. Our problem is to work out the three-letter setting for the Enigma. Of course, a message can be coded first, and then sent by cipher using the Enigma. It’s rare, but it really provides a headache. A double headache,’ he said and smiled to indicate he had made a joke.
Ned said: ‘I thought there were dozens of different ciphers — Hydra, Medusa, Thetis, Neptun and so on for the Navy…’
‘Oh yes, for all the German services. These are the three-letter settings. The more important the cipher, the more difficult the setting. Look at the machine and you’ll realize that one three-letter setting is not necessarily as easy as another.’
The trio grouped round him at the little table. ‘Just a simple wooden box, and when you open the lid you see — ’ he swung it up and back on its hinge as though to reveal a white rabbit, ‘what looks like a complicated portable typewriter. And in many ways that’s what it is, electrically operated.
‘In front, you have an ordinary typewriter keyboard — Q,W,E,R,T,Y and so on. Then behind it, where you’d expect to find the platen, is this board with all the letters reproduced again, each behind a tiny glass window and in the same order. And then behind that you see the three small slots with metal wheels showing, each with a sort of thin disc, with a cogwheel rim, next to it. Now look carefully — ’
Ned leaned over as Jenson opened a small cover.
‘What do you see, Commander?’
‘Letters of the alphabet are engraved round the rim of each wheel.’
‘Exactly, and let’s call that the rotor. But you can see — ’ he turned the rotors beside the engraved rims, ‘that each rotor is fitted to it own disc. Actually, we call the rim and disc together a rotor. You see three are fitted together here in the middle, but there are two more over in this rack on the right: they are spares or, rather, alternatives: the machine has five rotors but only uses three at any given time.’
‘How does wireless operator Schmidt know which three to use?’ the Croupier asked.
‘The sequence is changed every twenty-four hours, so his manual tells him that for, say, the fifth of November he uses rotors number one, four and five. So he fits those — it’s a simple pull-out and drop-in affair — depending on the date. Schmidt then picks up the call sign COD which shows the signal is for his own Panzer Division, and he copies it down as it comes over the wireless in Morse.
‘Then — I’m guessing now — he takes his handwritten signal to the Enigma operator, who will set his machine to the same setting as the OKW Enigma was when it scrambled — enciphered, rather — this particular signal. There’s another step too, but I’ll explain that later.’
‘How do the Germans actually pass messages to U-boats on this thing?’ Ned
‘Out in the Western Desert, wireless operator Schmidt listening on his frequency hears the letters COD in Morse, recognizes it as the call sign of the 15th Panzer division and copies down the Morse signal. It is, of course, the letters COD followed by what seems to be gibberish.
‘That signal is then taken to the 15th Panzer division’s Enigma. Right at the beginning of the message, following COD, is another three-letter group which tells what the machine should be set at, and, if it is very secret, an indication that it must be deciphered by an officer. I’ll show you all that on the machine in a moment.’
‘As easy as that, eh?’ Jemmy grunted.
‘If you have an Enigma, and if you have the appropriate manual for the cipher being used and can set the machine correctly. For the eavesdropper — us, in fact, — it’s more complex. We can usually work out for whom the signal is intended. Our problem is to work out the three-letter setting for the Enigma. Of course, a message can be coded first, and then sent by cipher using the Enigma. It’s rare, but it really provides a headache. A double headache,’ he said and smiled to indicate he had made a joke.
Ned said: ‘I thought there were dozens of different ciphers — Hydra, Medusa, Thetis, Neptun and so on for the Navy…’
‘Oh yes, for all the German services. These are the three-letter settings. The more important the cipher, the more difficult the setting. Look at the machine and you’ll realize that one three-letter setting is not necessarily as easy as another.’
The trio grouped round him at the little table. ‘Just a simple wooden box, and when you open the lid you see — ’ he swung it up and back on its hinge as though to reveal a white rabbit, ‘what looks like a complicated portable typewriter. And in many ways that’s what it is, electrically operated.
‘In front, you have an ordinary typewriter keyboard — Q,W,E,R,T,Y and so on. Then behind it, where you’d expect to find the platen, is this board with all the letters reproduced again, each behind a tiny glass window and in the same order. And then behind that you see the three small slots with metal wheels showing, each with a sort of thin disc, with a cogwheel rim, next to it. Now look carefully — ’
Ned leaned over as Jenson opened a small cover.
‘What do you see, Commander?’
‘Letters of the alphabet are engraved round the rim of each wheel.’
‘Exactly, and let’s call that the rotor. But you can see — ’ he turned the rotors beside the engraved rims, ‘that each rotor is fitted to it own disc. Actually, we call the rim and disc together a rotor. You see three are fitted together here in the middle, but there are two more over in this rack on the right: they are spares or, rather, alternatives: the machine has five rotors but only uses three at any given time.’
‘How does wireless operator Schmidt know which three to use?’ the Croupier asked.
‘The sequence is changed every twenty-four hours, so his manual tells him that for, say, the fifth of November he uses rotors number one, four and five. So he fits those — it’s a simple pull-out and drop-in affair — depending on the date. Schmidt then picks up the call sign COD which shows the signal is for his own Panzer Division, and he copies it down as it comes over the wireless in Morse.
‘Then — I’m guessing now — he takes his handwritten signal to the Enigma operator, who will set his machine to the same setting as the OKW Enigma was when it scrambled — enciphered, rather — this particular signal. There’s another step too, but I’ll explain that later.’
‘How do the Germans actually pass messages to U-boats on this thing?’ Ned
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