On the left is CDR Rodger Winn, the head of the Admiralty's Operational Intelligence Center - On the right, his counterpart on the COMINCH staff, CDR Kenneth Knowles

Historian David Kohnen's book Commanders Winn and Knowles: Winning the U-boat War with Intelligence 1939-1943 provides an excellent explaination of the development and working of the Admiralty and COMINCH Operational Intelligence Centers.  It is highly recommended as a companion to the records presented in this section. The book is puplished by The Enigma Press, April 2 1999, ISBN 8386110341

        A post war study of Allied communications intelligence in the U-boat war can be found in another document from Record Group 457 - Battle of the Atlantic: Allied Communication Intelligence December 1942 - May 1945.  This document has been transcribed and presented on the web by Patrick Clancey of the HyperWar Project.

       The reader's attention is called to Chapter II: The U-boat and Allied Naval Communication Intelligence, page 20 which contains a table titled: Record of U-boat Traffic Decryption (Atlantic) December 1942--May 1945.  This table gives the time late of decrypting U-boat messages by Op-20-G for each month of the war.  Time late is key to understanding the usefulness of the information derived from decryption of U-boat wireless traffic.  It is important to note that while Op-20-G (or Bletchly Park) could decrypt the text of a U-boat message, the naval grid square was further encoded.  The OICs had to work out the actual grid square based on other information such as D/F, interaction with Allied units and their understanding of U-boat operations.  The capture of the code book used to encode naval grid squares aboard U-505 in June 1944 enabled the OICs to read the actual naval grid square without guesswork or delay.