Secret Life of Bletchley Park - McKay Sinclair [44]
The one-ton machine was installed in Hut 1 on 18 March 1940. It did not immediately prove to be the answer to Allied prayers; indeed, it achieved very little in terms of key-setting results. The essence of the machine was that, like a giant calculator, it cycled through every possible combination of the three Enigma code wheels. When the machine hit the menu provided to the bombe operator by the cryptographer it would hit a ‘stop’. There would be good ‘stops’ and bad ‘stops’, which would all have to be checked.
There would be little unintentional outbreaks of assistance from the Germans, examples of idleness that provided invaluable clues. There were Enigma operators who ended each message with the proclamation: ‘Heil Hitler!’ and others who started each communication with a list of names for which it was intended. However, the first breaks into a new key were very difficult.
Alan Turing’s friend – and briefly, fiancée – Joan Murray worked specifically on naval Enigma and made much use of Victory early in 1940. The messages that were decoded turned out not to be of much direct value, but they did allow intelligence to build good background information about the navy itself. The work was gruelling; Joan and Turing often had to go through each of the possible 336 wheel orders.
Soon, however, a crucial breakthrough was made in the design of the bombe machines. This time the credit went to Gordon Welchman, as Andrew Hodges described in his biography of Alan Turing: ‘on studying the Turing bombe design, he saw that it failed to exploit Enigma weakness to the full … Welchman not only saw the possibility of improvement, but quickly solved the problem of how to incorporate the further implications into a mechanical process.’ It required only a piece of electrical circuitry – soon to be called ‘the diagonal board … the following of implications could still be achieved by the virtually instantaneous flow of electricity into a connected circuit’. Hodges continued:
Welchman could hardly believe that he had solved the problem, but drew a rough wiring diagram and convinced himself that it would work. Hurrying to the Cottage, he showed it to Alan, who was also incredulous at first, but rapidly became equally excited about the possibilities it opened up. It was a spectacular improvement … With the addition of a diagonal board, the bombe would enjoy an almost uncanny elegance and power.2
On 9 April 1940, the Germans landed in both Denmark and Norway with 15,000 troops, catching the British completely by surprise. Indeed, only four days beforehand, British ships had set sail in order to lay mines in Norwegian waters, prompting Neville Chamberlain to prematurely declare that ‘Hitler has missed the bus.’
The following month saw the German invasion of Belgium, Holland, Luxembourg and then, with astonishing and appalling speed, France – a full-scale offensive every bit as brutal as that against Poland. The British Expeditionary Force was encircled and nudged back towards Dunkirk. Prime Minister Neville Chamberlain resigned, and the government collapsed beneath him.
On 10 May Winston Churchill became Prime Minister, heading a National Government. Although the French had been under the impression that the British would leave a force behind, he immediately ordered the evacuation of British forces across the Channel. Then came the fall of Paris; and if one reads the many British Mass Observation diaries now, one is left in no doubt that the British were convinced that they were next.
The country was in a state of agonised suspense. From Mass Observation to the diaries of society figures such as Harold Nicolson, there is