For years, Saudi Arabia has been a major buyer of U.S.-made weapons. That relationship intensified after President Trump took office, with the American leader pushing oil-rich Riyadh to buy more weapons and Saudi Arabia pledging a purchase of $110 billion in U.S. arms just months after his inauguration.

After this weekend, when a devastating attack on Saudi oil facilities blindsided the kingdom, some observers were left wondering what protection Riyadh’s outreach to the United States has bought it.

Notwithstanding the expensive military hardware purchased by Saudi Arabia, experts say, the Saturday attack represented an unusually well-planned operation that would have been difficult for even the most well-equipped and experienced countries to detect and neutralize.

“This was a really flawless attack,” said Michael Knights, a scholar at the Washington Institute for Near East Policy who has followed Saudi air defense for decades, adding that evidence suggests that only one of 20 missiles may have missed its target. “That’s astounding.”

While in Ankara, Turkey, President Vladimir Putin said Sept. 16 Russia was ready to help Saudi Arabia following attacks on the its oil industry. (Reuters)

The attack has been claimed by Houthi insurgents in Yemen, where a Saudi-led coalition has been staging a troubled intervention since 2015. U.S. officials have suggested that at least part of the attack was launched from Iran, Saudi Arabia’s rival across the Persian Gulf.

The operation appeared to circumvent the defenses of Saudi Arabia’s military, including the six battalions of Patriot missile defense systems produced by U.S. defense contractor Raytheon — each of which can cost in the region of $1 billion.

Russian President Vladimir Putin responded to Saturday’s attack with mockery. At an event Monday in Turkey, Putin suggested that Saudi Arabia buy the Russian-made S-300 or S-400 missile defense system, as Iran and Turkey had done. “They will reliably protect all infrastructure objects of Saudi Arabia,” Putin said.

Iranian President Hassan Rouhani, also in attendance at the event, was seen grinning at the remarks.

The S-400 system is untested in real-life situations, but it costs less than the Patriot system and has technical features that are, on paper at least, an improvement on the U.S. system, including a longer range and the ability to operate in any direction.

Although Saudi Arabia once flirted with the idea of buying the S-400 system, it was probably aware that doing so would have a disastrous effect on its relationship with the Trump administration.

There is no evidence that the S-400, if deployed, could have handled Saturday’s incident better than the Patriot system. Even the best missile defense system cannot have a 100 percent success rate; shooting a moving target out of the sky is fundamentally difficult, requiring considerable speed and accuracy.

When Saudi officials claimed to have shot down a ballistic missile fired by the Houthis in 2017, a team of researchers argued in a report that the Patriot system, in fact, had done nothing to stop the missile, which had nearly hit its target — Riyadh’s airport.

Saturday’s attack would have been exponentially harder to neutralize than the 2017 strike. Both drones and cruise missiles appeared to have been used, with suggestions that the weapons were launched from multiple locations.

Knight said Saudi Arabia’s missile defense system was developed in the 1990s after watching the Iran-Iraq war and the Persian Gulf War, where airplanes and ballistic missiles were the main threat and could be spotted with radar easily, to be targeted by defense systems at a distance.

However, cruise missiles and drones fly far closer to the ground, making them harder for radar to detect. Given the low altitude, shooting one down carries greater risk, especially when detected late. “If you are wrong, you just blew up a British Airways flight,” Knights said.

Saudi Arabia has several missile defense systems that can target a low-altitude flight. Thomas Karako, a senior fellow at the Center for Strategic and International Studies, said that in theory the Patriot system could protect against such a threat, although it is primarily designed for ballistic missiles.

However, it would depend where it was placed. “The defended area for a Patriot battery is relatively small,” Karako said. “There are real limits, even if you have a ton of Patriots, on what you can defend.”

It is unclear whether the targeted oil facilities, in Khurais and Abqaiq, were defended by Patriot batteries or other systems.

Becca Wasser, a senior policy analyst at Rand Corp., said responsibility for protecting Saudi Arabia’s critical infrastructure was split between the Interior Ministry and the domestically focused Saudi Arabian National Guard, rather than the military.

“These overlapping structures, roles and responsibilities are really a vestige of coup-proofing practices,” Wasser said, designed to prevent any one wing of power from posing a threat to the ruling family.

Saudi Arabia is planning military reforms to address such problems, she added, part of society-wide changes being pushed by Crown Prince Mohammed bin Salman. The kingdom, aware of the technical threat posed by Iran to key facilities, may also seek to purchase new weapons that could combat the threat better.

The Iron Dome missile defense system, co-designed by the Israeli defense firm Rafael and Raytheon, may be one possibility, Karako said. The system is best known for its use in Israel, where it is used to shoot down rockets from Gaza and southern Lebanon. “The Saudis want to get something like Iron Dome, but they probably won’t call it Iron Dome,” Karako said.

Saudi Arabia also may seek to improve its radar capabilities with the use of elevated sensors that can detect threats from farther away.

For the time being, however, the country may have to learn to make better use of what it has already. New purchases from the United States could take years to go through, especially given a Congress increasingly suspicious of Saudi Arabia and export restrictions in place on some of the more advanced U.S. technology.

There may not be any handouts from the White House. Though Trump pushed the Saudi military to make more purchases, he suggested Monday that the United States did not have an obligation to protect the kingdom — and that if there was a conflict, Riyadh would again foot the bill.

“The fact is that the Saudis are going to have a lot of involvement in this if we decide to do something. They’ll be very much involved, and that includes payment,” Trump said.