ABSTRACT
After the First World War the British government reviewed the lessons learnt in breaking German codes. It decided to establish a new unit called the Government Code and Cypher School (GC&CS), ostensibly 'to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision' but also, in a secret clause, 'to study the methods of cypher communications used by foreign powers': in other words to break and read their signals traffic. GC&CS, an inter-service unit, was to operate under the overall control of the Admiralty in the person of its Director of Naval Intelligence, Commodore (later Admiral) Hugh Sinclair, nicknamed 'Quex'.
