Initially employed to check the personal columns of "The Times" for coded spy messages, in 1940 she was recruited to work as a codebreaker at Bletchley Park. She worked as an assistant to Dilly Knox, and was closely involved in the decryption effort before the Battle of Matapan. According to "The Daily Telegraph", she became so familiar with the styles of individual enemy operators that she could determine that two of them had a girlfriend called Rosa and this insight allowed her to develop a successful technique.