The Pentagon is testing portable 3D-printing labs in Hawaii that let U.S. soldiers design, print and assemble FPV drones in a matter of hours—turning vulnerable supply lines into on-demand battlefield factories. The ability to produce these user-guided munitions quickly is seen as crucial in any Pacific conflict, where logistics could be easily disrupted. WSJ joined the U.S. military on Oahu to see how troops are preparing for a new era of war dominated by drones. Chapters: 0:00 On the ground