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 contains a message from C to the Assistant Chief of Air Staff Intelligence (ACASI), 2266/T20, also see 2576, with the Prime Minister's (PM) comment; a report of the movement of German Air Force (GAF) units to airfields chosen for operations against England, on March 4; and the Chief of the Air Staff (CAS) forwards intelligence comments.