TAIPEI — A helicopter hot-refueling drill in Taiwan’s landmark military exercise shows how the island is preparing for drone threats when its choppers fly in and out of vulnerable forward positions, a danger repeatedly demonstrated in Ukraine.

Counter-drone ground teams, crouching amid the grass and on a nearby road, watched the skies on the seventh day of the 10-day Han Kuang exercise, as the 601st Air Cavalry Brigade of Taiwan’s army refueled three choppers by a lake in Taoyuan.

Armed with 5.56mm assault rifles and bulky anti-drone guns, the infantry provided cover for the three rotorcraft swooping in at low altitude for a top-up: an AH-64E…