Secret Life of Bletchley Park - McKay Sinclair [19]
In the interwar period, the Government Code and Cypher School (as Room 40, reduced to a small number of codebreakers, was now known) had moved to Broadway Buildings and devoted itself largely to dealing with Soviet codes. Dilly Knox was especially adept in this area. Bolshevism, together with Stalin’s colossal ambition, was understood to be the most pervasive threat to the national interests. With Hitler’s seizure of power in Germany in 1933, however, those geopolitical tectonic plates shifted very rapidly.
The German navy had been using Enigma since 1926. The machine itself – the basic model of rotating letter wheels with electric contact studs, keyboard and lampboard with illuminated letters, all looking a little like a typewriter – was adapted by German electrical engineer Arthur Scherbius from an earlier, simpler design.
Enigma had been on the market since 1923, when it was used by a few commercial banks to make sure their communications were kept secret. Too few commercial banks, though: the machine was a commercial failure. Curiously, in 1926 the British government purchased one model after the machine was demonstrated at the Foreign Office. The War Office, felt, however, that it would be too ungainly for use in the field.
Once the German navy acquired the system, Enigma was completely taken off the open market, both military and commercial; the Germans then set about making a series of modifications that would make the machine’s security very much tighter. Soon afterwards, the system was adopted by the German air force, and then by the army. The British War Office had been perfectly wrong about it. The machine was brilliantly portable; thousands were manufactured.
The principle of Enigma was that the machines both enciphered messages and, at the other end, deciphered them. The operator would type a letter on the normal-looking keyboard; a couple of seconds later, via an electric current sent through the rotating code-letter wheels, another letter on the adjacent lampboard would be illuminated. This substitute letter would be noted. And so on through all the letters of a message. The enciphered version would then be radioed in Morse to its intended recipient.
The recipient, with his Enigma machine set up in exactly the same way, would tap these encoded letters in, one by one – and one by one, the real letters would be illuminated on the lampboard.
‘Although it would have been possible for one cipher clerk to carry out all the tasks of the enciphering procedure himself,’ noted codebreaker Alan Stripp, ‘this would have been a lengthy and confusing process; normally it called for a team of two.’ Even with two, it was a time-consuming business. On top of this, the machine settings would be changed every twenty-four hours.
In 1927, GC&CS took the wise precaution of studying their basic, wholly unmodified Enigma machine. Hugh Foss – eventually to become a Bletchley leading light, brilliant at Japanese decrypts – was the man assigned to the job.
John Herivel later noted, in a tone of obvious admiration, the intricate innards of this aesthetically intriguing machine: ‘the function of the [letter] wheels with their studs, pins, rings and serrated flanges, how they could be taken in and out of the scrambler, the function of the left-hand reflector drum’ and ‘the wonderfully ingenious way each of the three wheels was forced into the nearest of 26 equally spaced “allowable” positions where they were firmly held, yet not so firmly that they could not be turned by finger pressure on the flanges to any one of the 25 other allowable positions’.4
And so this neat machine of bakelite and brass was an irresistibly beguiling prospect for any mathematician or logician. Even if the machine settings were being changed daily, there surely had to be some means by which the device could be defeated?
But there was an extra difficulty. The new German version had what was known as a stecker-board, or plug board, which made the machine’s wiring vastly more complex, and