What Happened Yemen's Houthi rebel forces killed at least 40 people Aug. 1 in a complex attack on a military parade in the port city of Aden involving a ballistic missile and drone. The victims included members of the Security Belt, a local force trained and supported by the United Arab Emirates. Eyewitnesses said the ballistic missile struck directly behind the speaker's dais after a general had just concluded a speech. The Houthis said they used a medium-range ballistic missile and an explosives-laden Qasef-2K drone to conduct the attack, which killed Brig. Gen. Monier al Yafie. Why It Matters Tactically, the incident highlights the Houthis' ability to launch sophisticated and deadly attacks throughout Yemen . Its coordinated nature establishes that the Houthis are becoming more proficient at executing attacks using ballistic missiles and drones, capabilities the Houthis have and will use in future attacks in Yemen and Saudi Arabia.