At least five American-made Patriot missiles apparently missed, malfunctioned, or otherwise failed when Saudi forces tried to intercept a barrage of rockets targeting Riyadh on March 25.

That's bad news for the US military and its closest allies, who are counting on the Patriot to stop large-scale enemy attacks during a major war.

The ground-launched, radar-guided Patriot missile, which is 19 feet long in its basic version, has been controversial since shortly after its introduction in 1984. It missed many of its targets during the 1991 Gulf War. Twelve years later during the US-led invasion of Iraq, Patriot crews shot down two allied warplanes, killing three crew members.

"It's nothing but an unbroken trail of disasters with this weapon system," Theodore Postol, an MIT physicist and prominent critic of US missile defenses, told me.

Rebel forces from the Houthi group, which has taken over much of Yemen in recent years, fired at least seven rockets at Saudi Arabia on the night of March 25. Saudi Arabia leads a coalition of Middle East countries battling the Houthis in Yemen.

The Saudi military launched Patriot Advanced Capability-2 missiles in an attempt to destroy the Houthi rockets in mid-air. The Saudis claimed seven of the Patriots struck their targets.

One man reportedly died after being struck by metal fragments. It's unclear whether the fragments came from a malfunctioning Patriot, a successful intercept or a Houthi rockets striking the ground.

Amateur videos that appeared online in the aftermath of the missile skirmish indicate that many of the Patriots—which are manufactured by US firm Raytheon—exploded in mid-air or veered off course.

The same thing happened during the 1991 Gulf War, said Postol, a former Pentagon science advisor. "It seems in 25 years they haven't fixed it."

The Patriot flies a straight trajectory for the first four seconds after launch, during which time the missile accelerates past the sound barrier. The missile has a habit of malfunctioning during those initial seconds in the air. Of the apparent five separate Patriot launches that appear in videos from Riydah, two seem to have ended in premature explosions during the acceleration phase, Postol pointed out.

After four seconds in the air, a Patriot begins maneuvering and searching for a signal from the ground-based radar that helps to guide it. Three of the Saudi Patriots appear to have malfunctioned during this phase of flight. "They suddenly went downward and exploded," Postol said.

The failures over Saudi Arabia last weekend could point to a design flaw that critics such as Postol have been trying for decades to fix. "In the Gulf War of 1991, we definitely saw Patriots take off, turn around and dive to ground in both Saudi Arabia and in Israel," Postol told me.

"When we reported what we saw in videos from Israel, Raytheon claimed this only occured in Israel because the Israelis didn't know what they were doing. Then we uncovered videos of the missiles doing the same thing in Saudi Arabia."

Raytheon did not respond to a request for comment. In 2018, the US Defense Department set aside $1.1 billion to buy 240 Patriot missiles.

Patriots continued to malfunction in 2003. US Army Patriot crews mistakenly shot down a US Navy F/A-18 fighter and a British Royal Air Force Tornado bomber, killing the American pilot and both British crew members. Coalition aircrews grew to fear their own air-defenses.

“The Patriots scared the Hell out of us,” one F-16 pilot remarked. Another F-16 pilot actually fired a missile at a US Patriot system after the Patriot crew locked onto the F-16 with its radar.

Postol blamed the 2003 incidents on a combination of poor training and technical flaws in the Patriot. Like many air-defense systems, the Patriot searches for radio-transponder signals in an effort to separate allied warplanes from enemy ones. Following the 2003 shoot-downs, the U.S.-led coalition ordered its aircrews to switch to more reliable transponders that the Patriots hopefully would be better able to detect.

As recently as 2010, the US Missile Defense Agency claimed it had improved the Patriot. "Over the past decade the United States has made significant progress in developing and fielding essential capabilities for protection against attack from short- and medium-range ballistic missiles," the agency reported. "These capabilities include increasingly capable Patriot batteries."

The Missile Defense Agency did not respond to a request for comment.

Multiple failures on the part of Saudi Arabia's Patriots could indicate that, in fact, the air-defense system hasn't gotten much better since its inauspicious 1991 debut and subsequent friendly-fire incidents in 2003. That could jeopardize the safety of US and allied forces in a future conflict.