Bantam Press, 1st ed., 2001. Xv + 543 pp., photo-plates. D.j., 24 x 16cm. FINE. The brilliant work carried out by British codebreakers based at Bletchley Park is now believed to have shortened the duration of the Second World War by up to two years. But during the dark days of 1941, as Britain stood almost alone against the apparently unstoppable tide of the Nazi war machine, this remarkable achievement seemed a million miles away. In October 1941, four of the leading codebreakers appealed to Churchill for more staff. He responded by insisting that they be given everything they needed, adding the succinct instruction : "Action This Day." It was to be a key turning point for the codebreakers and the war itself. The editors, both leading authorities on the subject, have assembled a number of key writers, including several of those who worked at Bletchley Park and some who have only now agreed to tell their story, to explain its importance in the history of twentieth-century codebreaking and the birth of today’s computer age.