The ‘nice, loyal’ girl who helped us crack Hitler

Margaret Rock (bottom left) in her Portsmouth High School days
Margaret Rock (bottom left) in her Portsmouth High School days
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When Miss Ada Cossey, the headmistress of Portsmouth High School for Girls, sat at her desk on June 22, 1920 to write a reference for Margaret Alice Rock’s university application, she could see a promising student ‘with exceedingly good abilities’.

However, she could never have predicted what this petite 16-year-old student with a natural talent for mathematics would achieve for her country in the Second World War as a Bletchley Park code breaker.

‘I can recommend Margaret Rock very warmly,’ Miss Cossey wrote on Portsmouth High School headed paper with a sweep of her informal handwriting. She describes Margaret as ‘thoughtful, nice, good and loyal.’

Margaret’s father, a member of the Royal Navy’s Special Reserve of Officers, was called up in 1914 as a medical doctor. He died off the coast of Ireland when his ship, SS Laurentic, struck a mine in January 1917 and sank within an hour along with its 43 tonnes of gold bullion.

This would have been devastating to the close and loving Rock family, who by now had moved to Portsmouth.

Later that year, Margaret’s mother continued to encourage her children’s educational success and helped Margaret secure a scholarship at Portsmouth High School in Kent Road, Southsea.

There, Margaret was able to overcome the grief of losing her father and find a passion for mathematics.

Margaret’s BA Honours Degree in mathematics and French from University of London’s Bedford College as well as her post-graduation work in statistics ensured her application for a job with the Foreign Office was accepted.

It would appear she was introduced to codebreaking by her paratrooper brother John Frank Rock, a war hero who was to die in a gliding accident in 1942.

On April 15, 1940, Margaret arrived at Bletchley Park, where she was selected to work in Dillwyn (Dilly) Knox’s Research Section, a small team tasked with breaking untried ‘Enigma machine variations’ and later the German armed forces intelligence service (Abwehr) Enigmas.

In October 1941 Dilly finally understood how one variation of the Abwehr Enigma machine worked and the first message was read on December 8.

By this time Margaret was billeted in Bletchley and working with Dilly at his home in Courns Wood, Buckinghamshire. When she returned to her duties at Bletchley Park, the team had been renamed ISK (Illicit Services Knox).

Life continued and it is a testament to their hard work that ISK solved more than 140,000 codes during the war.

Margaret received an MBE for her services to the country in 1945, but her name has only recently been discovered on the Scholars Board and Examinations Board hanging in Portsmouth High School.

Now with the discovery of Margaret Rock’s personal papers, a book of letters will shed new light on this enigmatic code breaker and offer a unique insight into her life during the Second World War.

The book, Margaret Rock by Kerry Howard (, is supported by a website of background information. The book and website ( will be available from Thursday.