The arrival of ‘Captain Ridley’s Shooting Party’ at a mansion house in the Buckinghamshire countryside in late August 1938 was to set the scene for one of the most remarkable stories of World War Two. They had an air of friends enjoying a relaxed weekend together at a country house. They even brought with them one of the best chefs at the Savoy Hotel to cook their food. But the small group of people who turned up at Bletchley Park were far from relaxed or ordinary.
They were members of MI6, and the Government Code and Cypher School (GC&CS), a secret team of individuals including a number of scholars turned codebreaker’s. Their job; to see whether Bletchley Park would work as a wartime location, well away from London, for intelligence activity by GC&CS as well as elements of MI6.
The GC&CS mission was to crack the Nazi codes and ciphers. The most famous of the cipher systems to be broken at Bletchley Park was the Enigma. There were also a large number of lower-level German systems to break as well as those of Hitler’s allies. At the start of the war in September 1939 the codebreaker’s returned to Bletchley Park to begin their war-winning work in earnest
The Poles had broken Enigma in 1932, when the encoding machine was undergoing trials with the German Army. But when the Poles broke Enigma, the cipher altered only once every few months. With the advent of war, it changed at least once a day, giving 159 million million million possible settings to choose from. The Poles decided to inform the British in July 1939 once they needed help to break Enigma and with invasion of Poland imminent.
As more and more people arrived to join the code breaking operations, the various sections began to move into large pre-fabricated wooden huts set up on the lawns of the Park. For security reasons, the various sections were known only by their hut numbers.
The first operational break into Enigma came around the 23 January 1940, when the team working under Dilly Knox, with the mathematicians John Jeffrey’s, Peter Twinn and Alan Turing, unravelled the German Army administrative key that became known at Bletchley Park as ‘The Green’. Encouraged by this success, the codebreaker’s managed to crack the ‘Red’ key used by the Luftwaffe liaison officer’s coordinating air support for army units.
Gordon Welchman, soon to become head of the Army and Air Force section, devised a system whereby his codebreakers were supported by other staff based in a neighbouring hut, which turned the deciphered messages into intelligence reports.