It was Sept 4, 1939, the day after the UK declared war on Germany, when mathematician Alan Turing reported to work at the Government Code and Cypher School at Bletchley Park. Within weeks of his arrival, Turing and his colleagues were able to intercept high-level encrypted enemy communication signals and decode a vast number of these messages. The intelligence gleaned from this effort was passed on to field commanders, a process that was decisive to Allied victory.