Unmanned systems with a variable degree of autonomy, generally known as ‘drones,’ have become commonplace in the world’s advanced militaries. In their various aerial, maritime, and ground forms, these vehicles are used to perform a wide spectrum of roles. Yet advances in new technologies such as artificial intelligence (AI), robotics, and data fusion may revolutionize their employment by enabling large numbers of drones to operate in a coordinated and reactive manner. If fully developed, this concept – known as ‘swarming’ – could have profound tactical and strategic effects; possibly to the point of changing the nature of warfare in the 21st century.