Since 2003, the United States has spent billions of dollars developing a spectrum of defensive weapons to stop powerful ballistic missiles from striking U.S. bases and positions. But on Jan. 8, none of those defenses were present when volleys of Iranian ballistic missiles came plunging down on an Iraqi air base that housed U.S. service members.

The attack on Ain al-Asad air base was a predictable response by Iran to the U.S. drone strike that killed Iranian Maj. Gen. Qassem Soleimani days earlier. But the roughly 1,500 U.S. military personnel at the base could only pray that none of the nearly 4-ton missiles landed nearby.

It remains a stark failure that no attempt was made to provide the 5,000 U.S. military personnel in Iraq with an active ballistic missile defense.

The earthshaking attack highlights how little forethought went into the consequences of killing Soleimani, and how that recklessness might easily have cost the lives of U.S. military personnel. At the very least, the Defense Department ought to have extended to its forces in Iraq the same protection it has provided Saudi Arabia — by covering them with advanced Patriot missile defenses.

Indeed, U.S troops in Iraq should have received the same consideration the moment the Trump administration committed to killing Soleimani and provoking Iran. It already had evidence that Iran was willing to use the weapons to strike foreign targets. And U.S. personnel in Iraq had already been frequent targets of smaller rocket attacks — including one just a week earlier, when Iran orchestrated the storming of the U.S. Embassy compound in Baghdad.

The U.S. military has 60 batteries of Patriot surface-to-air missiles capable of intercepting short-range ballistic missiles and seven higher-end THAAD systems designed to intercept higher-flying missiles. Those batteries are in high demand around the globe, with about half already committed overseas.

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Some argue that the Army simply doesn’t have enough air defense units to go around, and it’s true that U.S. forces defending bases in Saudi Arabia and elsewhere across the Middle East were also within striking distance of Iran’s many short-range ballistic missiles. They, too, merit the Patriots protecting them.

But in April 2019, the Pentagon rapid-deployed one of its few THAAD batteries to Israel for an exercise. Granted, there are additional complexities in deploying such a system and the troops that accompany it to Iraq, but are we supposed to believe the U.S. military couldn’t rush air defense units in a crisis when it had already done so for an exercise?

And just last fall, following an attack by Iranian cruise missiles and drones that had briefly crippled Saudi oil production over the summer, the Pentagon deployed a Patriot battery and air defense radars to buttress Saudi defenses and to better protect troops and aircraft also being dispatched to Saudi Arabia.

That no U.S. personnel died in the Iranian onslaught came down to a combination of advance notice — from early-warning satellites that alerted personnel at the base the moment the missiles arced into the sky and likely from sources in Iran — as well as sheer luck. Contrary to analyses claiming Tehran intentionally sought to avoid major casualties and damage, the chairman of the Joint Chiefs of Staff assessed that the attack was “intended to cause structural damage — destroy vehicles, equipment and aircraft — and kill personnel.”

As it happens, the Fateh missiles directed at Ain al-Asad landed multiple direct hits on structures across the base, incinerating personnel quarters and hangars alike. Although the warning thankfully allowed most personnel to evacuate to underground bunkers, a report by CNN makes it clear that not all of the Saddam Hussein-era bunkers were robust, and some personnel remained exposed as they staffed the perimeter to guard against a potential ground attack by pro-Iranian militias.

The threat from Iran’s ballistic missiles was no secret. Since 2017, Tehran has launched ballistic missiles at least four times to retaliate against enemies in Iraq, Israel and Syria. A missile strike in Iraq in September 2018 demonstrated deadly accuracy as multiple Fateh missiles precisely hit a compound in which Kurdish militants were meeting, according to Iranian reports, reportedly killing 18 people.

American complacency about providing adequate missile defenses to personnel in Iraq is all the more outrageous given that the Trump administration cited Iran’s ballistic missile development to justify exiting the nuclear deal with Tehran in 2018 — which worsened tension with Iran in the lead-up to Soleimani’s assassination.

To be sure, air defense missiles aren’t perfect. During the 1991 Persian Gulf War, U.S. Patriot missiles intercepted dozens of Iraqi Scuds. But several evaded interception, and one of them killed 27 Pennsylvania U.S. Army Reserve members when it struck their barracks in Riyadh, Saudi Arabia.

More recently, Saudi Arabia has used Patriot missiles to intercept more than 100 missile attacks from Houthi rebels in Yemen, with good but by no means perfect results. Still, each missile that gets knocked out of the sky is one less that has a chance to cause mass casualties.

Are we supposed to believe the U.S. military couldn’t rush air defense units in a crisis when it had already done so for an exercise?

It’s also true that each Patriot battery can defend only a relatively small bubble of airspace against ballistic missiles. So Iran might simply have shifted to a different target had Patriots defended Ain al-Asad. But compelling adversaries to attack less attractive targets is a form of success in itself.

Even if a perfect defense was impractical, it remains a stark failure that no attempt was made to provide the 5,000 U.S. military personnel in Iraq with an active ballistic missile defense under those circumstances — although the Pentagon may be making belated “adjustments.”

Because of the good fortune that no U.S. personnel were killed in the Iranian strike, the failure to deploy active defenses against ballistic missile attacks has not gotten the scrutiny it should have. But the United States might not be so lucky next time.

CORRECTION (Jan. 17, 2020, 6 p.m. ET): A previous version of this article misstated the military affiliation of the 27 soldiers killed by an Iraqi missile in the 1991 Persian Gulf War. They were part of a U.S. Army Reserve Unit based in Pennsylvania, not part of the Pennsylvania National Guard.