What is the theme in A Man Called Intrepid: The Secret War by William Stevenson?

Another recurring theme in the book was the need for secrecy. The British made decisions, like those regarding Dieppe and Coventry, based on the secrecy of the fact that they had an Enigma machine. They were intercepting German and Axis communications before they formally entered the war. The information that came from the Enigma was coded as ULTRA and they were always careful to hide the fact that their information was the result of the confiscated Enigma machine that they didn't want the Germans to know about. The British didn't even tell Stalin the source of their warnings about the Nazi invasion of Russia. He didn't believe their warnings because he didn't know the source of their information.