JERUSALEM — The attack on Saudi Arabia’s Abqaiq and Khurais oil facilities on Sept. 14 served as a reality check for countries struggling to define the level of the threat posed by drone swarms and low-altitude cruise missiles.

Now, in a region where that threat is particularly acute, countries are left to reexamine existing air defense technology.

According to the Saudi Defense Ministry, 18 drones and seven cruise missiles were fired at the kingdom in the early hours the day in mid-September.

The drones struck Abqaiq, a facility that the Center for Strategic and International Studies think tank had warned the month before was a potential critical infrastructure target. Several cruise missiles fell short and did not hit the facility. Four cruise missiles struck Khurais. Saudi and U.S. official blame on Iran, but the government there denies involvement.

What is clear is the failure of existing air defense systems to stop the attack.

The Abqaiq facility’s air defenses reportedly included the American-made Patriot system, Oerlikon GDF 35mm cannons equipped with the Skyguard radar and a version of France’s Crotale called Shahine. Satellite images posted by Michael Duitsman, a research associate at the James Martin Center for Nonproliferation Studies, shows the setup: Impeded by radar ranges and the facility itself, as well as the speed and angle of the drones and missiles, Saudi air defense apparently did not engage the drones.

“If U.S.-supplied air defenses were not oriented to defend against an attack from Iran, that’s incomprehensible. If they were, but they were not engaged, that’s incompetent. If they simply weren’t up to the task of preventing such precision attacks, that’s concerning,” said Daniel Shapiro, a former U.S. ambassador to Israel and a visiting fellow at the Institute for National Security Studies. “And it would seem to validate Israeli concerns that even effective air and missile defense systems, as Israel has, could be overwhelmed by a sufficient quantity of precision-guidance missiles.”

There is a debate about the level of this threat. Brig. Gen. Pini Yungman, a former air defense commander with the Israeli Air Force and current head of Rafael’s air defense systems division, contrasts the drone swarm with a cruise missile with a range of 1,000 kilometers and equipped with a large warhead. “Drones, even drone swarms, are not a strategic threat, even if you take dozens to attack. They carry a very low weight of bomb or ammunition,” Yungman said.

Uzi Rubin, former director of the state-run Israel Missile Defense Organization, doesn’t think what happened in Saudi Arabia could happen in Israel. “We have a smaller area, and that has an advantage in many respects because it is an advantage in controlling our airspace.”

He said the primary challenge in stopping an attack like that in Saudi Arabia is not the ability to shoot down the threats, but rather to detect the low-flying threats. “When it comes to missiles, missile defense sensors will aim above the horizon because the missile is above it and you don’t want clutter. So when it comes to guarding, the issue is things that can sneak in near the ground,” he explained.

The key, then, is to close the gap that potentially exists near the ground.

“It’s not too difficult to close the gap; the Saudis can do it with local defenses,” he asserted. But he acknowledged that the larger the land area, the more difficult it can be to maintain control.

Rubin said shooting down drone swarms can be accomplished with anti-aircraft guns, noting that Iraq downed several Tomahawk cruise missiles in 1991 after discovering their flight path.

“You don’t need anything fancy,” he said — the Russian SA-22 or Pantsir system, with 30mm cannons, missiles and infrared direction finders would do.

“I think once the surprise of the [Sept. 14] attack wears off, then one should sit back and see it is not a very devastating attack.” Like Yungman, he said a long-range precision missile aimed at a strategic facility like a nuclear reactor in a European country would be a more serious threat.

However, Thomas Karako, a senior fellow at the CSIS think tank, told Defense News that the attack suggests a dramatic escalation. “More broadly speaking, it is what I’ve been talking about: The specter of complex, integrated air and missile attack is not theoretical — it has arrived.”

He argues that the Abqaiq attack draws a “bright red line under the problem set” and that “we need a mix of active and passive measures, kinetic and non-kinetic to counter.”

“It’s not a technological problem, it’s an engineering problem,” he said. “You need to look beyond the horizon and look in every direction.” That would include 360 coverage by radar and elevated sensors.

Israel, the test bed

Yungman considers the Middle East, particularly Israel, to be a proving ground. Since the 1940s, a number of different weapons systems, many made in Western countries or the Soviet Union, were used in regional combat.

“In this region, the asymmetric threat became bigger. So in the north there are almost 200,000 short-range rockets and missiles and accurate missiles as a threat" from Hezbollah, he said. "And in Syria we can see accurate, maneuvering ballistic missiles and cruise missiles. So air defense and air missile defense became, from the asymmetric aspect, bigger and bigger, and the air defense system became an issue we need to invest in and develop as fast as we can."

With the support of the United States, Israel built and tested the Arrow system in the 1990s, becoming one layer of the country’s multilayered system that eventually included Arrow-2, Iron Dome and David’s Sling.

Short of using preemptive airstrikes against drone manufacturers and launch teams, Israel is upgrading its air defense on a “daily basis,” Yungman noted.

“The main threat is not face-to-face [combat] threats — it is rockets, drones, cruise missiles, maneuvering [theater ballistic missiles] and [short-range ballistic missiles] with big and small warheads. When we are talking about thousands or tens of thousands or more, it is very complicated, but it can be defeated,” he said.

One way to confront drone swarms involves soft-kill measures. Because drones are operated by GPS and radio control, jamming or taking control of the drone is one route.

But Rubin said what stands out about the Abqaiq incident is that the homing by the drones appeared to be optical, not GPS-guided.

Also noteworthy, evidence indicates that some of the UAVs weren’t carrying warheads, as they didn’t all explode.

Alternatively, a hard-kill approach might involve using a 5- to 10-kilowatt laser. Lasers can destroy drones up to 2.5 kilometers away, according to Yungman.

The U.S. has looked at lasers for its Stryker armored vehicles, and Germany, Russia and Turkey are among the nation-states developing the technology. Israel’s Rafael has been working on laser interceptors for years, including the Drone Dome laser-based intercept system.

“I can say that from 2 kilometers I could hit a drone the size of a penny,” Yungman claimed.

remains of Iranian cruise missiles and drones

Another option could be drone-on-drone combat, though that capability is still under development.

While systems like the Iron Dome are combat-proven, questions remain about their ability to confront a drone swarm.

In theory, when using radar and electro-optics, an air defense system should be able to cover the bands necessary to track the drones using several systems and 360-degree phased-array coverage.

“In our research and technology we have the radar and electro-optical and jamming, GPS-denying [capabilities],” Yungman said. “And we have the ability to kill it.”

Rubin described the attack on Saudi Arabia as a kind of “Pearl Harbor,” and it reminded him to an Aug. 17 attack on the Shaybah oil field in Saudi Arabia by Houthi rebels involving 10 drones.

“The surprise was not in the attack, but the audacity,” Rubin recalled, adding that a precision attack by drones doesn’t make the aircraft less vulnerable to air defense systems.

The Stunner interceptor missile of David’s Sling, for instance, has the capability to intercept drones, missiles and other ordnance, including low-flying cruise missiles. But for that to work, there can’t be a gap in the radar coverage, Rubin noted.

Certainly, the recent attack in Saudi Arabia will impact industry and spur development from the key players in this area of defense, according to Karako of CSIS.

“I think you’ll see global demand signal for a variety of means to counter these threats,” he said. “It will spark a lot of solutions.”

Seth J. Frantzman is the Israel correspondent for Defense News. He has covered conflict in the Mideast since 2010 for different publications. He has experience covering the international coalition against the Islamic State group in Iraq and Syria, and he is a co-founder and executive director of the Middle East Center for Reporting and Analysis.