In 1941, in response to a warning by four of Britain's codebreakers that their efforts to break the Enigma code were being hampered by lack of funds, Winston Churchill ordered that they be given everything they need. He marked his minutes of the decision with the words action this day. This book includes edited lectures by some of Britain's foremost historians, former codebreakers and academics, and tells the full history of Bletchley Park, the codebreaking base. The contributors trace the legacy of Bletchley, from the groundbreaking work which lead to the breaking of Enigma and other wartime codes, to the invention of modern computing, and its influence on Cold War codebreaking. The book also includes the human stories and personal reminiscences of former codebreakers who worked at Bletchley.