This well-edited collection of articles is an excellent addition to the growing literature on Bletchley Park's codebreaking achievements. There is a good deal of previously unpublished information and some interesting personal memoirs. There are summary articles that help place the wartime codebreaking triumphs in a much broader and more balanced perspective than earlier publications, and others that give some overdue recognition to contributions from organizations other than the better-known Enigma- and Tunny-breaking operations. The book also helps locate Bletchley's wartime achievements within a wider pre- and post-war context. Readers unfamiliar with the Bletchley Park story might want to read "Codebreakers" by Hinsley and Stripp as a prelude to "Action This Day".
I love this book as it is made up of individual articles charting the Government Code & Cypher School codebreaking operation at Bletchley Park during World War 2 and beyond. Most of the articles are written by those at Bletchley Park so it can't get more 'first hand' than that. There are also articles by leading experts and covers both the social and more technical aspects of codebreaking. Make sure you buy the latest version, as all proceeds go to Bletchley Park