Most of this volume describes the actual use of Special Intelligence material.
'...to avoid the pitfalls of of complacency (i), it is necessary to compare the handling and use of Sigint in the two World Wars ...'
(i) Example: 'The German brain is probably quite incapable of the imaginative and intuitive processes which 8E applied to Z material ... It is on these levels that intelligence becomes an art. Like architecture it escapes into a region above and beyond mathematics and logic'.
8E was a section of Hut 8 at BP, and Z material was German Enigma messages.