Intelligence officials also raised alarms about the potential for attacks on U.S. personnel in Jordan from Iran-backed groups, one of the officials said. Those concerns were part of a broader assessment made by the intelligence community that American troops and diplomats in the region were particularly vulnerable after the Gaza invasion.

While U.S. officials have said for years that the country’s air defenses have vulnerabilities, the latest warnings grew more urgent as Iran-backed militias stepped up their attacks in October and November.

That raises questions about whether the Pentagon could have done more to increase protections for troops at the Jordan outpost and other bases in the region in the days and weeks following Hamas’ Oct. 7 attack on Israel.

Tower 22 — the outpost where three service members were killed on Jan. 28 — had already been threatened at least once by a drone from an Iran-backed militias,
in October. In that case, its air defenses took out the enemy drone.

“In theory, DOD has had a few months to rectify the lack of defense, and it didn’t,” said Charles Lister, a senior fellow and the Director of the Syria and Countering Terrorism & Extremism programs at the Middle East Institute. “There is a precedent for an attack on the facility. And that should have rung alarm bells, that it was insufficiently defended.”

The U.S. has for years debated how to defend against increasingly available Iranian drones, which are difficult to detect due to their size, flight profile and small radar cross-section. The problem is that no one solution can provide 100 percent coverage, requiring many layers of capabilities that still fail to stop all of the threats.

The U.S. did take steps to reinforce defenses at Tower 22 after Israel’s October invasion. DOD reinforced Tower 22 with additional electronic warfare capability, increased protections for troops and conducted training rehearsals, said one DOD official with direct knowledge of the moves.

But Tower 22 may have had an additional vulnerability. Because the vast majority of attacks have been in Iraq and Syria, Tower 22 was not provided a “kinetic” counter-drone capability that many bases in those countries have, said the official and a second DOD official with direct knowledge of the discussions, confirming earlier reporting by the Washington Post. Instead, the base had “multiple” electronic warfare capabilities that enabled it to counter drones through jamming or disabling its systems.

Resources to Tower 22 were also limited because there are only so many air defense capabilities available for the region, the first DOD official said.

And it’s not clear that a kinetic capability would have thwarted the attack, particularly if the problem was that the drone was not even detected, said the first official.

Since the Jan. 28 attack, the Pentagon has beefed up the air defenses at the base, the officials said, declining to elaborate for operational security reasons.

Tom Karako, director of the Missile Defense Project at the Center for Strategic and International Studies, said the U.S. military is constantly short on the air defense systems it needs around the world.

“If you don’t have enough stuff to spread around, you’re not necessarily going to have [protection] everywhere,” Karako said, arguing that DOD needs to invest in improving training and strengthening bunkers in order to close the gap. “You’re never going to have enough stuff.”

The Pentagon is still investigating how the enemy drone evaded Tower 22’s air defenses. While a friendly drone did land at the same time, investigators now do not believe this was the reason the base’s air defenses missed the enemy drone, according to the first DOD official. It’s possible the drone was not detected due to its low flight path, the official said.

While no air defense system is perfect, the Pentagon has gotten significantly better at countering these drones in recent years, according to Defense Department officials and experts who have spent time in the region. Most bases in Iraq and Syria are now armed with kinetic capabilities that can shoot down incoming enemy drones, said Lister of the Middle East Institute.

There have been more than 160 Iran-backed attacks on U.S. troops in Syria, Iraq and Jordan since October, and U.S. air defenses have successfully taken out most of those threats, primarily drones and rockets, causing minimal damage to infrastructure or injuries to personnel.

“What happened at Tower 22, that was tragic, absolutely tragic,” Pentagon spokesperson Sabrina Singh told reporters Tuesday. “But for the most part our air defenses have been able to catch or been able to destroy any impact or any incoming from — whether it be rockets or drones, at bases.

In addition to the three service members killed at Tower 22, the attacks have injured another 143 people — 11 of them with serious or very serious injuries, according to Maj. Pete Nguyen, Department of Defense spokesperson.