When people think about the Second World War, they seldom think in terms of silence and small acts. This was a war in which the industry of entire nations was rearranged to feed fighting, and it was fought on a scale in which battles could include hundreds of thousands of combatants. Whole cities and populations were destroyed, with millions of casualties occurring at places like Leningrad.

But World War II was also a conflict in which modern covert operations first hit their stride. From the jungles of Burma to the streets of Paris, spies, saboteurs, and commandos carried out missions built on secrecy and cunning. Precise, self-contained operations could be as important to the outcome of the war as acts of massive destruction, whether it involved targeted assassinations, sabotaging key logistics, or counterintelligence to break up the enemy’s own rings. At the time, most of these operations were hidden from the public since that was the only way they could be successfully carried out, but in the years since, stories about various missions have emerged. They paint a picture of incredible courage and ingenuity, whether in war zones, enemy territory, or far from the front lines.

Though it might be hard to believe, the Americans did not have a covert operations organization when they joined the war, and like the British, it took them some time to realize it could be a powerful tool. In time, all the hard work led to the growth of the OSS into an organization with over 13,000 staff and 40 offices scattered across the world. Its purposes were initially similar to that of Britain’s Special Operations Executive, including espionage, sabotage, and intelligence assessments, but with time and experience, it expanded to include economic, psychological, and guerrilla warfare, as well as counter-intelligence work. And of course, it would all chart a path for the early days of America’s most famous intelligence agency, the CIA.