Inside Room 40
The Codebreakers of World War I

What the reviewers say:

Cryptologia:

Inside Room 40 presents a comprehensive view of World War I British signals intelligence ... It has a broader focus than most histories of Room 40. Although the emphasis in Gannon’s book is Room 40, he also considers the work of MI1(b) and the relationship between the two codebreaking agencies. ... There is enough material to understand how the codebook systems worked but not too much to cause a reader to skip the descriptions.


Institute of Engineering and Technology (IET) magazine:


The contribution made by the Government Code and Cypher School at Bletchley Park is well documented, but its First World War precursor has received much less attention. Paul Gannon’s newly-published book ‘Inside Room 40’ examines the activities of the code breaking class of 1916 ... the most intriguing part of Gannon’s finds in Room 40 files at the National Archives is that it devised some code-breaking machinery; this challenges the common perception that the Colossus and Bombe of Bletchley Park (the subject of Gannon’s previous history) constituted the origins of mechanised – and indeed computerised – code cracking.


Radio Society of Great Britain:

Inside Room 40 is based on previously secret files which bring to life the hidden history of the British code breakers. From the very earliest luck of capturing a German Naval code book from a hapless German cruiser which ran aground in August 1914, through to the deciphering of the famous "Zimmermann" telegram that brought the United States into the 1st World War, it is all chronicled here. ... As coding technology developed so did Room 40. Inside Room 40 details the methods used in code breaking, along with the early tabulating machines that were the forerunners of the "Colossus" computer famously used at Bletchley to break German codes in WWII. For those who are unaware of the huge contribution made to the war effort by the code breakers of Room 40 this hardback book is a revelation. Inside Room 40 provides a detailed and comprehensive view of this little known area of WWI history.


Amazon reader review: * * * * *

I was impressed with Paul's book 'Colossus' so I was expecting something of comparable quality with this book. I was not disappointed. The author has a knack for presenting his subjects in a broad perspective, with plenty of external information to put the material in their full contemporary context. Also useful were the mini biographies of several of the personalities mentioned. The icing on the cake is his revelation that Hollerith punched card machines were used to store data. A very enjoyable and worthwhile read.



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