Why are Houthi missiles breaking through Saudi Arabia’s air defences? 

Yemen’s Houthis, the armed group also known as Ansar Allah (Arabic for Supporters of God), are hitting deep inside Saudi Arabia with waves of ballistic missiles, cruise missiles and drones.

Riyadh’s King Khalid International Airport has been targeted multiple times by the Houthis since their new military campaign against the kingdom began in September.

An attack on the airport on Saturday killed 12 people and wounded 309, the deadliest attack in the kingdom in more than a decade. Saudi Arabia’s civil aviation authority was forced to suspend operations and diverted all flights, while the United States and United Kingdom issued new travel warnings for citizens.

The Houthis claimed two other attacks on the air hub earlier this week and on Sunday warned people to avoid Saudi airports.

Houthi weaponry

Saudi Arabia possesses one of the best-equipped militaries in the world, boasting advanced, multilayered air defence systems.

Saudi warplanes have pummelled Houthi positions across Yemen in the past week, seeking to roll back the Iran-backed group’s recent advances against the Yemeni government army, which Riyadh supports.

The Houthis’ own arsenal has come a long way 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 particular targets such as Saudi airports and oil facilities.

Here’s what we know about the Houthis’ weaponry, how their tactics have changed and why Saudi air defences are struggling to keep pace.

How advanced is the Houthi arsenal?

The exact type of weapon used to attack Riyadh airport is unknown, but the Houthis have fired hundreds of drones and missiles at Saudi Arabia since the 2015 intervention. The Iran-backed group has also targeted Israel and allegedly Israeli-linked vessels since the start of the genocide in Gaza in October 2023.

The group has used its weapons in concert, mixing drones and missiles of varying speeds to confound air defences. The same mix has shaped Yemen’s ground war, with the Houthis pounding government positions for weeks before seizing the Red Sea coast in a rapid offensive last month.

Among the group’s most advanced options are medium-range ballistic missiles such as the Palestine-2, a two-stage solid fuel missile believed to have a range of 2,000km with hypersonic capabilities. Another is the Toufan, which appears to be a rebranded Iranian Ghadr missile, thought to have a range of between 1,350km and 1,950km.

The reach of those missiles – some carrying cluster warheads – has allowed the Houthis to breach Israel’s air defence network, some 2,000 km from Yemen.

The Houthis also maintain a number of short-range missiles, such as their Burkan and Badr series. They are also believed to be of Iranian origin and have been used in cross-border strikes into Saudi Arabia.

According to Nawaf Obaid, a senior fellow at Kings College War Studies Department, the Houthis’ missile arsenal is essentially derived from Iranian weaponry, with some Chinese technological influences.

“The Houthis have demonstrated little evidence of significant indigenous technological innovation,” he said. “Their domestic capabilities are largely confined to producing certain lower-end missiles and drones.”

Last month, Yemen’s government forces alleged that the Houthis have been receiving help from the Iranian Revolutionary Guard Corps (IRGC) to develop a new capability – loitering cruise missiles.

Why are Saudi defences struggling to keep up?

Saudi authorities say their forces shot down a number of projectiles over the past week, including a pair of ballistic missiles aimed at the capital on Thursday. But they failed to intercept the projectile that hit Riyadh’s King Khalid International Airport on Saturday.

Nawaf Obaid told Al Jazeera that occasional penetration of Saudi air defences is to be expected, given the size of the kingdom and its border with Yemen.

“As much as you can have a multi-layered air defence system, one will always come through,” he said, pointing out that dozens of Houthi attempts are thwarted for each successful attack.

Wolfgang Pusztai, a security policy and defence analyst, told Al Jazeera that the main focus of Saudi Arabia’s ballistic missile defence system was countering threats from Iran.

However, as the attacks from the Houthis increase, he views it as likely that the Saudis are re-orienting some of these defences towards Yemen.

There is also the issue of interceptor stocks. Saudi Arabia – along with many of the United States’ regional and global allies – has struggled with limited stockpiles of Patriot and THAAD munitions. These were rapidly expended by the US and its allies during the early months of the war with Iran.

Last month, Riyadh had reportedly reached out to a number of friendly countries to deploy air defence or other support to help defend against attacks by the Houthis.

Limitations

However, the Houthis are also fighting under serious constraints. The group is under a UN-mandated arms embargo, a years-long Saudi blockade, as well as fighting on several fronts across Yemen.

“Militarily, the Saudi-led coalition has the upper hand, but the Houthis can still dominate the headlines with occasional strikes against 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 disproportionately visible.”

The exact size of the Houthis’ missile arsenal is unknown, calling into question the group’s ability to sustain attacks on Saudi Arabia, while simultaneously fighting a fierce ground war where missiles and drones have been used by the Iran-backed group.

Obaid said that Saudi Arabia’s air campaign in Yemen has focused heavily on targeting the group’s missile depots, underground installations and drone production facilities. The group is “inflicting enormous damage” on the Houthis’ military capabilities, he added.

Pusztai told Al Jazeera that the Houthis likely have just a limited number of short-range ballistic missiles left.

This would mean they would be incapable of launching saturation attacks, where multiple missiles and drones are fired at targets, such as in Saudi Arabia.

Instead, they could focus on aiming single missiles at less-defended civilian targets “to maximise the strategic impact of these attacks, in this case to disrupt civilian air traffic”.