SANA'A, Aug. 17 -- The port director of al-Makha spent most of Saturday watching his operations come to a halt for the third consecutive day. Houthi missiles had struck the Red Sea city's outskirts and main road, killing four people and wounding eight. A thousand kilometers to the northeast in Marib, the afternoon had been marked by a different kind of sound: six ballistic missiles and four drones tearing into residential neighborhoods, wounding four civilians and destroying a bakery in the Al-Sharika district. By nightfall on August 16, two more Yemeni cities had joined the growing list of places where the country's civil war, silent for four years, had begun to speak again.

The attacks are the most visible face of a Houthi military cam...