Government Code and Cypher School: Signals Intelligence Passed to the Prime Minister, Messages and Correspondence

A file of signals intelligence reports, messages, and correspondence issued by the Government Code and Cypher School and sent by the head ('C') of the Secret Intelligence Service (MI6) to the Prime Minister, Winston Churchill. This file includes the following correspondence: a message to the First Sea Lord (ISL) from C concerning the Prime Minister's comments on the Naval Headlines. These contained instructions to U-boats about action to be taken against warships in a specified area. This file also includes the ISL's response.