A recent military exercise by the Russian Armed Forces in the Mediterranean has given the world its best look yet at the Zircon hypersonic missile—a weapon shrouded in mystery and speculation. Until now, this missile had only been seen in brief glimpses or as fragments after alleged combat tests in Ukraine. But this time, Russia provided clearer footage, raising new questions about the Zircon's capabilities and its role in modern warfare.

The drills also highlight the growing challenges ...