Stalin’s USSR was a nation obsessed with secrecy and highly experienced in the skills of espionage. But despite establishing networks of agents across Europe and the Far East in the 1930s, the Soviets were still caught off-guard by Hitler’s invasion in 1941. But thereafter, the GRU (army intelligence) and NKVD (KGB forerunner) went on to score some amazing intelligence coups in Tokyo, Washington, and even from the heart of Berlin.