Alfred Dillwyn Knox is not a widely recognised name, but his career as one of the UK’s leading cryptologists and codebreakers spanned some 30 years, and two world wars. For much of that time he lived in Naphill, and was a well-known and congenial figure in the locality. Dilly, as he was known, was born in Oxford on July 23 July, 1884, the fourth of six children of the Revd Edmund Arbuthnott Knox and his first wife, Ellen French. He went to Eton College as a King’s Scholar, became “Captain of School” and won the school’s main prize for mathematics. In 1903 he went to King’s College at Cambridge University, obtaining a first class degree of the classical tripos.