The U.S. Army Combat Capabilities Development Command Army Research Laboratory (DEVCOM ARL) disclosed on November 2 that it has completed flight verification of a 3D-printed heavy-fuel rotary engine. The metal additively manufactured engine, paired with a motor-generator in a series hybrid power system, was flight-tested on a Group 3 unmanned aircraft system (UAS); the military calls it the first 3D-printed heavy-fuel engine. The project falls under ARL's Versatile Tactical Power and Propulsion basic research program, which aims to enable UAS to fly longer and faster. Metal printing allowed the research team to rapidly iterate on the air-cooled engine design and accelerate validation of heavy-fuel applications in small UAS power systems. Heavy fuel, a kerosene/diesel-class fuel, is safer than gasoline and simplifies logistics, making it the direction for standardizing military UAS propulsion. This marks the Army's latest milestone in advancing additive manufacturing for power systems and echoes earlier 3D-printing production moves for small turbojet engines by companies such as Beehive Industries, showing that metal additive manufacturing is moving from structural parts into rotating machinery and core powertrain components. Demand for validation and serial production of superalloy and titanium alloy powders in military propulsion applications is expected to keep rising.