The study of writing and solving codes is Cryptologists use maths find patterns in codes and solve them. When the Second World War broke out, there were around 150 people working at Bletchley Park, but this quickly grew to about 10,000. In 1945, 75% of the workers were women, but only some were code-breakers. One of them was Joan Clarke. She was very good at mathematics and helped to break some of the most difficult codes during the war.