DUBAI, Aug. 25 -- For eighteen months, the Houthi movement has been attacking ships in the Red Sea and the Gulf of Aden, and for most of that time, Saudi Arabia watched from the margins. That changed Sunday when Houthi forces fired a ballistic missile at a Saudi-flagged tanker navigating the kingdom's own coastal waters, then announced that Saudi ships are no longer safe to sail at all.

The missile struck the tanker approximately 63 nautical miles west of Yanbu, igniting a fire on the vessel's main deck. The UK Maritime Trade Operations authority, which monitors maritime security across the Indian Ocean and Red Sea, confirmed the incident and said all crew members were safe and no environmental damage had been reported. The vessel's iden...