The Authorized History of MI5 (Britain’s secret service). Listened to book on CD while commuting.
Very long, very detailed account of the organization, insofar as the author was able to compile within the bounds of secrecy restrictions. If you think back as to what occurred in the world since the establishment of MI5 in 1909, you can probably guess at what parts of the book were interesting and what parts were dull. World War I and II and double-crossing the Germans = interesting; countering communist subversion and Soviet espionage + Irish and Islamic terrorism = not as interesting. This book was a little too long to be recommendable to just anyone. Maybe there are better books focusing on just the interesting time periods, and we can leave “Defend the Realm” to the historians interested in the whole account.
In 1915, during World War I, the British captured a German agent named Muller. Rather than putting him on trial or such, they pretended he had infiltrated successfully, and sent reports back to the Germans as if they were Muller, feeding false information. This worked pretty well until the Germans caught on after several months. They even periodically sent money to fund “Muller’s” spying activities. MI5 used the funds to purchase the agency’s first automobile … which they named “the Muller.” 🙂
During World War II, the “double-cross” system was matured. Shortly after the outbreak of war, (although they didn’t entirely know it at the time), MI5 controlled all German agents within Britain. (!) They came up with a sophisticated system of using the agents to report back some actual intelligence, designed to impress the Germans but not harm British war efforts, mixed with manufactured dis-information. This worked spectacularly well throughout the war. The biggest achievement was in leading the Germans to believe the main Overlord attack would occur at Calais rather than Normandy. German High Command reinforced Calais, and refused to greatly diminish their defenses there even after Normandy was invaded, thinking that Normandy was just a feint. By the time they realized there would be no Calais attack, several days later, it was too late and the Allies already had an unbreakable beachhead.
Later, during the V-1 attacks on London, the double-cross spies reported that the missiles were overshooting central London, when they were really slightly undershooting. This caused the Germans to adjust their aim such that they were undershooting even more, sparing more of London from damage. Very clever.
If you read this book for fun, just read up until the end of World War II and skip or skim the rest.