Why Houthi Missiles Are Piercing Saudi Arabia's Air Defenses

Yemen's Houthi movement, also known as Ansar Allah, is using coordinated waves of ballistic missiles, cruise missiles and drones to strike deep inside Saudi Arabia. King Khalid International Airport in Riyadh has repeatedly been targeted since the Houthis launched a new military campaign against the kingdom in September.

Saturday's strike on the airport killed 12 people and wounded 309, making it the bloodiest attack on Saudi Arabia in more than a decade. The kingdom's civil aviation authority was forced to suspend operations and divert all flights, while the United States and Britain issued fresh travel advisories for their citizens.

The Houthis claimed two other attacks on the same airport earlier in the week, and on Sunday again warned people to stay away from Saudi airports.

The Houthi arsenal

Saudi Arabia has one of the best-equipped militaries in the world, with a modern, multi-layered air defense network. Its warplanes have bombed Houthi positions across Yemen over the past week, seeking to roll back recent advances by the Iran-backed group against Yemeni government forces that Riyadh supports.

The Houthi arsenal has grown substantially since the group seized control of Sanaa from the government in September 2014. Their drones and missiles have reached as far as Israel and, as their accuracy has shown, can hit specific targets such as Saudi airports and oil facilities.

How advanced is the Houthi arsenal?

It is not yet clear which weapons were used in the Riyadh airport attack, but the Houthis have fired hundreds of drones and missiles at Saudi Arabia since the coalition intervened in 2015. The Iran-backed group has also targeted Israel and ships alleged to have links to Israel since the conflict in Gaza erupted in October 2023.

The Houthis use a mix of weapons, blending drones and missiles of differing speeds to confuse air defense systems. That approach has also shaped the ground war in Yemen, where the Houthis pounded government positions for weeks before rapidly seizing Red Sea coastal territory in last month's offensive.

Among their most advanced weapons is the medium-range Palestine-2 ballistic missile, a two-stage solid-fuel system reported to have a range of 2,000 km and hypersonic capability. Another is the Toufan, seemingly a renamed version of Iran's Ghadr missile, with a reported range of 1,350 to 1,950 km.

The range of these missiles, including variants carrying cluster warheads, has allowed the Houthis to penetrate Israel's air defense network from roughly 2,000 km away in Yemen.

The Houthis also maintain a range of short-range missiles such as the Burkan and Badr lines, also reported to be of Iranian origin and previously used in cross-border attacks on Saudi Arabia.

According to Nawaf Obaid, a senior fellow at the Department of War Studies at King's College London, the Houthi missile stockpile is essentially derived from Iranian weapons, with some Chinese technological influence. "The Houthis show very little evidence of significant indigenous technological innovation. Their domestic capability is largely limited to producing some low-segment missiles and UAVs," he said.

Last month, Yemeni government forces accused the Houthis of receiving support from Iran's Islamic Revolutionary Guard Corps (IRGC) to develop a new capability: loitering cruise missiles.

Why is Saudi air defense struggling to keep up?

Saudi authorities say their forces shot down multiple flying objects over the past week, including two ballistic missiles aimed at the capital on Thursday. However, they failed to intercept the object that struck King Khalid International Airport on Saturday.

Nawaf Obaid told Al Jazeera that occasional breaches of Saudi air defenses are to be expected, given the kingdom's vast territory and its border with Yemen. "No matter how layered your air defense is, there will always be one that gets through," he said, noting that dozens of Houthi attempts are stopped for every successful strike.

Wolfgang Pusztai, a security and defense policy analyst, told Al Jazeera that the primary focus of Saudi ballistic missile defense is countering threats from Iran. But as attacks from the Houthis mount, he said, Saudi Arabia is likely shifting part of its defensive posture toward Yemen.

Interceptor stockpiles are another concern. Saudi Arabia, along with many regional and global US allies, is grappling with limited Patriot and THAAD inventories that were depleted quickly during the first months of the war with Iran. Last month, Riyadh was reported to have approached several friendly countries to deploy air defense or other support to help defend against Houthi attacks.

The limits

The Houthis, however, are also fighting under severe constraints. The group is subject to a United Nations arms embargo, a years-long Saudi blockade, and must fight on multiple fronts across Yemen.

"Militarily, the Saudi-led coalition has the upper hand, but the Houthis can still grab headlines with occasional strikes on Saudi Arabia," Obaid said. "As the world's largest crude oil exporter and a G20 economy, Saudi Arabia carries global responsibilities that make such attacks especially visible."

The precise size of the Houthi missile stockpile remains unknown, raising questions about the group's ability to sustain attacks on Saudi Arabia while simultaneously fighting intense ground battles in which both missiles and drones are used.

Obaid said Saudi airstrikes in Yemen are heavily focused on the group's missile depots, underground facilities and drone production sites. He added that the campaign is inflicting "enormous damage" on Houthi military capabilities.

Pusztai told Al Jazeera the Houthis may have only a limited number of short-range ballistic missiles left. That means they are unlikely to be able to launch saturation attacks, in which many missiles and drones rain down on a target at once, as seen in Saudi Arabia. Instead, they may focus on firing individual missiles at less-protected civilian targets "to maximize strategic impact, in this case disrupting civil aviation."