Margaret Rock was born in Portsmouth in 1903. She was a talented mathematician and in 1939 she went to work for the Government Code and Cypher School (CCCS) at Bletchley Park. Bletchley was selected simply as being more or less equidistant from Oxford University and Cambridge University since the Foreign Office believed that university staff made the best cryptographers. The house itself was a large Victorian Tudor-Gothic mansion, whose ample grounds sloped down to the railway station. (1)
Margaret went to work for Alfred Dilwyn Knox. As the most senior cryptographer at the GCCS was allocated working space in "a row of chunky converted interlinked houses - just across the courtyard from the main house, near the stables". It became known as the "Cottage". (2) At first his department consisted of ten people, including "two very brilliant" young women, Margaret Rock and Mavis Batey. (3) Mavis later recalled. "We were all thrown in the deep end. No one knew how the blessed thing worked. When I first arrived, I was told, 'We are breaking machines, have you got a pencil? And that was it. You got no explanation. I never saw an Enigma machine. Dilly Knox was able to reduce it - I won't say to a game, but a sort of linguistic puzzle. It was rather like driving a car while having no idea what goes on under the bonnet." (4) "We were looking at new traffic all the time or where the wheels or the wiring had been changed, or at other new techniques. So you had to work it all out yourself from scratch.” (5)
Knox admitted that he liked employing women. According to Sinclair McKay, the author of The Secret Life of Bletchley Park (2010): "Dilwyn Knox... found that women had a greater aptitude for the work required - as well as nimbleness of mind and capacity for lateral thought, they possessed a care and attention to detail that many men might not have had." (6) Knox definitely had a very enlightened approach to the employment of women and was accused of being guilty of "positive discrimination".
Knox was so impressed with the work of Margaret Rock and Mavis Batey that in August 1940, that he contacted head office: "Miss Lever (Batey) is the most capable and the most useful and if there is any scheme of selection for a small advancement in wages, her name should be considered.... Miss Rock is 4th or 5th best in the whole Enigma staff and quite as useful as some of the professors." (7)
Some members of staff at Bletchley Park suggested that Knox selected so many women to join his team because he liked to be surrounded by attractive women who were given the name "Dilly's Fillies". One of these women later pointed out: "A myth has grown up that Dilly went around in 1939 looking at the girls arriving at Bletchley and picking the most attractive for the Cottage... That is completely untrue. Dilly took us on our qualifications." (8)
Margaret Rock died in 1983.
Mavis Batey vividly recalls the V-1 rockets and the means by which the codebreakers at Bletchley Park sought to thwart them. "We were working on double agents all the time, giving misinformation to their controllers. And because we could read the Enigma, we could see how they were receiving this misinformation. One of the things when the Vls started was that the double agent was asked to give a report to the Germans on where the rockets were falling. Because of course they were wanting them to fall on central London.
"At that point, the bombs werefalling in central London so intelligence here wanted them to cut out at a different point. So this double agent was instructed to tell his masters that they were falling north of London. The result of this was that the Germans cut the range back a little and as a result, the rockets started falling in south London. Just where my parents lived."
In this case, it seemed that to Mrs Batey at least, ignorance was preferable to any other state; for security reasons, she knew nothing of this double-cross operation, or the messages that confirmed its success. "I had no idea and it is just as well that I didn't. So when I saw the devastation at Norbury, I did not know that it had anything to do with anything I was doing. It really would have been a terrible shock to know that."