Because of the secrecy that enveloped the U.S. Office of Strategic Services in World War II, it surprises most people, including nearby residents, to learn that spies were trained in some of the National Parks-not just spies but guerrilla leaders, saboteurs, clandestine radio operators and others who would be infiltrated behind enemy lines. What are today known as Catoctin Mountain Park in Maryland and Prince William Forest Park in Virginia played a vital role in the training of the operatives of the U.S. Office of Strategic Services. Known by its initials, the OSS was a specially created wartime military agency that fought a largely invisible and covert war against the Axis powers between 1942 and 1945. America's first national centralized intelligence agency with thousands of clandestine operatives, spies, and intelligence analysts, the OSS is acknowledged as the predecessor of the Central Intelligence Agency. With its Special Operations troops and Operational Group commandos, the OSS is also widely considered a forerunner of today's Special Forces. From 1941 to 1945, the men and women of the OSS were part of a "shadow war," a war largely behind the scenes and often behind enemy lines around the world. Highly secret during the war and in many instances for years thereafter, that effort was designed to help undermine the conquests of Nazi Germany, fascist Italy, and militaristic Japan. The "shadow warriors" sought to supply and guide local resistance movements, demoralize the enemy through "black propaganda," and to gather intelligence and commit sabotage in enemy occupied territory to contribute to the victory of the Allies' armed forces as they overcame the totalitarian, Axis aggressors.