Catalogue description Report on the work of B1B in connection with the use of ISOS material and counter...

Report on the work of B1B in connection with the use of ISOS material and counter espionage methods in Gibraltar in the War 1939-1945. This report was written after the war by Herbert HART, the head of MI5's B1B section. This small MI5 section was its link with SIS, the Radio Security Service and Bletchley Park on German signals intelligence. The report makes clear that the initial ISOS breakthrough was directly attributable to intelligence gained from the early war double agent case, SNOW. The file contains lists and statistics of German spies identified from ISOS intercepts and gives details of a number who may have slipped through the net despite investigation, as well as fabricated agents who almost certainly never existed. Despite the file's title the subject matter ranges far more widely than Gibraltar