6. THE CODEBREAKERS OF BLETCHLEY PARK
As soon as their homeland was invaded in September 1939, several Polish mathematicians escaped to the west with the secrets of the German ‘Enigma’ encryption device. This scrambled all 26 letters of the alphabet to a pre-set key that changed every 24 hours. From the May 1940 invasion of France onwards, German reports – essentially transmitted in Enigma gibberish – were intercepted over the air and forwarded by outstations to Bletchley Park, near Milton Keynes in Buckinghamshire, which housed the UK Government Code and Cypher School and the intelligence programme known as ‘Ultra’.
Several brilliant minds at Bletchley helped devise ‘bombes’: electromechanical devices designed to discover the daily settings of Enigma machines. From March 1940, these increased the pace that German messages could be deciphered, translated into English and assessed for their military importance. Understanding Enigma traffic contributed to victory in the Battle of Britain, assessing the German threats to invade England, and was especially important during the battle of the Atlantic, on which British survival depended in 1941–42.
Enigma provided tactical intelligence of mostly short-term value. More longterm insights into the German military mind were gleaned from mid-1941, when senior commanders started transmitting coded orders to one another using the ‘Lorenz’ wireless teleprinter, whose traffic was nicknamed ‘Tunny’. This gave access to strategic intentions and was initially deciphered by brainpower alone, until the creation of ‘Colossus’, the world’s first programmable digital electronic computer, which commenced operations in February 1944.
It is challenging to measure the precise value of the work done at Bletchley, where Italian and Japanese traffic was also broken. We do know that on 12 July 1945, US general and future president Dwight D Eisenhower wrote a secret letter to thank Sir Stewart Menzies, who had kept both Churchill and Eisenhower supplied with daily Ultra material. In it, he stated: “The intelligence which has emanated from you before and during this campaign has been of priceless value to me… It has saved thousands of British and American lives, and in no small way contributed to the speed with which the enemy was routed and eventually forced to surrender.”
This was reinforced by Sir Harry Hinsley, a former Bletchley man and later author of the official volumes on British Intelligence in the Second World War. He stated that, without Ultra, “the war would have been something like two years longer, perhaps three years longer, possibly four years longer than it was”.