ABSTRACT
Why this great emphasis on sigint? What is so special about it? What about the other ways of finding out what the enemy, 'the man over the hilF, to use the Duke of Wellington's words, is up to? Surely spies, captured documents and the interrogation of prisoners are all tried and tested methods, joined more recently by aerial photography and, even nearer to our own times, satellite surveillance? The answer is that all of these have their value, and intelligence is at its best when it draws together the results of all reliable probings, both to complement and to check each other. But most of the other methods have inbuilt limitations which hardly apply to sigint.
