Mavis Batey explains how Margaret Rock’s Canary Islands Service Enigma break in May 1943.
Anyone familiar with the Bletchley Park story has heard of Mavis Batey (formerly Mavis Lever) and her extraordinary role as one of the few women codebreakers at Bletchley Park during World War 2.
She has written about her boss and mentor, legendary eccentric codebreaker Dilly Knox in her brilliant book Dilly – the man who broke Enigmas. The book is a fascinating insight into his quirky character and is a unique view of the groundbreaking work carried out by Dilly and his girls in Cottage No.3, including Mavis’ own codebreaking success that put the Italian Navy out of the war following the Battle of Matapan.
You can find out more about Mavis’ Dilly book in my post 5 Great Bletchley Books to buy.
Since the release of the official history of how the Abwehr (German Military Intelligence) Enigma machines ciphers were broken, Mavis has been assisting the codebreaking community and enthusiasts understand its technical contents. The document was presented to Mavis in September 2011 and is known as ‘Batey Batey Rock and Twinn‘ (BBRT) after its four authors. They are Mavis Batey, Keith Batey, Margaret Rock and Peter Twinn, who were all part of Dilly’s Research Section in the Cottage and later, ISK (Illicit Services Knox).
I plan to visit The National Archives over the coming weeks to see the document and try to identify Margaret Rock’s contributions (not that I’m likely to understand it!). Mavis has kindly provided me with an outline of how Margaret broke a Canary Islands Service cipher in 1943, which pages are referred to in BBRT on pages 79-83.
In May 1943 Margaret succeeded in breaking the wheel wiring of a new Abwehr machine service from Paris to the Canary Islands . There were so few messages that it had not been tackled before but as with Dilly who had left the scene a problem was a problem and there to be solved.
Peter Twinn, who had replaced Dilly as head of the section, said it was done with ‘great mental dexterity’, considering the scanty amount of evidence. One routine daily message of approximately the same length was identified as a weather report and as words always ended with an X an attempt was made to find these, bearing in mind that on the Enigma machine one letter can never encipher as itself.
As with everything Dilly’s girls did, it required infinite patience and it was a great shame that sometimes the messages turned out to be worthless. Margaret’s Canary Islands break did however add to the tricks of the trade and would have pleased Dilly greatly.
Mavis Batey, September 2013
You can find out more about Mavis Batey on the Women Codebreakers page.