This book is dedicated to the 100th anniversary of the formation of the Special Departments of the Cheka–KGB–FSB (1918–2018). The author of the book briefly talks about the main stages of the development and formation of Russian military counterintelligence. For the first time, archival materials have been introduced into historical circulation, shedding light on the activities of military counterintelligence during the Great Patriotic War. The book is intended for historians, political scientists, students, and all those who are not indifferent to the history of domestic intelligence services.