World War II: British MI5 Report on Counter Espionage Methods - Download

World War II: British MI5 Report on Counter Espionage Methods

Report on the work of MI5's B1B in connection with the use of ISOS material and counter espionage methods in Gibraltar from 1939-1945.

The acronym ISOS stood for Intelligence Service Oliver Strachey, Strachey being the veteran codebreaker at Bletchley Park who had broken the Abwehr ciphers. 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. MI5’s B1B section analyzed decrypted communications picked up from German military intelligence.

He shows that the initial break of Abwehr ciphers was made possible by intelligence obtained early in the war from Double Agent SNOW.

Arthur Graham Owens was a Welsh-born electrical engineer spying for the Germans, whom it codenamed SNOW. Shortly after the outbreak of War, SNOW became the first in a series of 120 wartime German agents who were turned by MI5 into double agents.

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.