In an unassuming town outside Detroit, a small American startup is quietly preparing U.S. troops for the next era of warfare — where battles won’t be fought by soldiers, but by swarms of machines.

In an unassuming town outside Detroit, a small American startup is quietly preparing U.S. troops for the next era of warfare — where battles won’t be fought by soldiers but by swarms of machines.

American defense planners are racing to catch up in a fight that is still mostly invisible to the public: the contest to control the skies with cheap, expendable drones that can fly in coordinated ...