New Delhi, Nov. 1 -- At a secret location in rural Ukraine, columns of attack drones are assembled at night and in near silence to strike deep inside Russia.

Their targets are strategic: oil refineries, fuel depots, and military logistics hubs. Since the summer, Ukraine's long-range drone campaign has ramped up dramatically, pounding energy infrastructure across Russia and stretching Moscow's air defenses thin.

Built from parts made in a scattered network of workshops, these drones now fly much further than at any point in the war.

Officers in body armor move with quick precision; headlamps glow red to stay hidden. Engines sputter like old motorcycles as exhaust fumes drift into the moonless night. Minutes later, one after another, the...