Saudi Arabia on Saturday said its air-defense system destroyed an armed Houthi drone that was flying in Yemen’s airspace. The drone was judged to be a threat to Saudi Arabia and its forces, which are fighting against the Iranian-backed Houthis in Yemen.Over the years, Iran has helped the Houthi rebels in Yemen build up a drone army. These include mostly what are called “loitering munitions,” or kamikaze drones, which means they are fed coordinates to a target and fly into it, much like a cruise missile. While some can loiter over a target, it does not appear that most of these drones have the ability to return to Houthi bases after a mission.Iran has been improving its drones, adding missiles and other technology to them and increasing their range. Some advanced drones in Yemen reportedly can even reach Israel. Whether that is true has not been verified. However, when it comes to Saudi Arabia, the Iran drone threat is deadly serious. Riyadh also has challenges identifying where the drones come from. This is partly an air-defense problem. The kingdom is a large country and needs a lot of radar and air-defense installations to both detect and seek out the drones to destroy.On January 23, a report noted that Saudi Arabia had intercepted an “apparent missile or drone attack” near Riyadh. Reports at the time suggested the attack might have come from Iraq.The Iraqi front is interesting because Iran has sent drones to its allies there, including Kataib Hezbollah, which was blamed for a May 2019 attack. They may have used an area near Jurf al-Sakhar to store the drones and control them. The drones struck two pumping stations in Saudi Arabia.Add to this the September 2019 swarm attack in which Iran used drones and cruise missiles, flying over Iraq or Kuwait to strike Abqaiq in Saudi Arabia, and the pattern is clear: Riyadh faces a major drone threat. Saudi Arabia has become a testing ground for how a country can create multilayered and integrated air defense to stop the drones. The problem for Riyadh is that its frontline is immense.From the deserts near Yemen to areas facing Kuwait and Iraq, there are thousands of kilometers that drones can penetrate. All Iran’s allies have to do is find a weak spot in the air defenses. Ultimately, radar and air defense don’t have an endless range, and it is difficult to plug all the gaps.Riyadh, a key ally of the US, may get advice on how best to continue to confront the threats. Evidence shows that it has done a good job downing drones and missiles in recent years.The question is whether the threats will grow as Tehran seeks to target US allies to put pressure on them and Washington and to test new weapons.