Israel’s southern population came under attack once again in November 2019. The Iran-backed terrorist group Palestinian Islamic Jihad (PIJ) fired more than 450 rockets into Israel from the Gaza Strip. Israelis sprinted to shelters, and the Iron Dome air-defense system once again shielded them from the onslaught. Thousands of miles from the action, sitting in the back seat of an Uber, I was on the phone with an Israeli official on the Gaza border who explained to me, without hesitation, that Israel had picked this fight.

There would be no attempt to spin this, the official said, even as rockets hurtled across the sky above him. Israel fired first, he said, by liquidating Baha Abu al-Ata, the PIJ military commander in the Gaza Strip. Israel tracked him for months, but he always surrounded himself with human shields. So the Israelis stalked him—and when, at last, he failed to shield himself with living human bodies, they struck with deadly precision. The Israeli Air Force did not just isolate its strike to the building, or the floor of the building, or the room on that floor. It struck al-Ata in his bed, reportedly with only his wife at his side. No one else in the building was hurt.

PIJ, in consultation with the group’s paymasters in Tehran, responded with predictable ferocity. Yet as rocket fire increased, and even when occasional volleys pierced the Iron Dome’s defenses (one struck a highway near the town of Ashdod, narrowly missing traffic), Israel’s decision makers demonstrated remarkable restraint. As the official on the phone explained to me, the Israeli Air Force was calmly and selectively taking out PIJ military leaders and operatives when they had a clear shot. The majority of the bombing runs, however, were aimed at PIJ rocket stores. “We’re hunting rockets,” the official said flatly.

That kind of cool-headed discipline would not be possible without the Iron Dome system. When rockets are prevented from hitting their intended targets, Israeli officials don’t hear calls from the public to send in ground troops. And for most defense officials (at least in this current government), there is no desire to escalate in Gaza. Even as it takes out occasional targets of opportunity, Israel prefers to keep its powder dry. The real danger lies to the north, where a brutal conflict is brewing.

Over the past five years, the Israelis have been fighting a quiet war nearly every night. During what is now known as the “Campaign Between Wars” or “War Between Wars,” the Israelis have taken out high-value targets—more than 200 of them, according to estimates published last year, and it’s probably closer to 300 now—from Syria and Iraq to Lebanon and beyond. As early as 2013, the Israelis spoke euphemistically about such strikes, noting that they were targeting “game-changing weapons” that Iran was transferring to its proxies amid the chaos of Syria’s civil war.

Recently, the Israelis have become much more specific. Their targets are precision-guided munitions, or PGMs.

Until now, Israel has been blessed with ill-equipped enemies. The efforts of Iranian proxies such as Hamas, Hezbollah, and PIJ have been mitigated by Iron Dome, which has an 86 percent success rate (some Israeli officials say it’s even higher) in neutralizing incoming enemy projectiles. That rate is boosted by the fact that Israel’s foes have been firing unguided, or “dumb,” rockets. Without GPS or target-acquisition capabilities, many of these rockets undershoot or overshoot their intended targets. When Iron Dome assesses a rocket’s errant trajectory, it declines to intercept it and allows it to explode in an uninhabited space.

Iran is now working overtime to establish a program that will allow its proxies to convert their dumb rockets into smart ones. The United States began a process of converting its own unguided rockets into PGMs back in the late 1990s. The Israelis utilized similar technology. The result was the deadly Joint Direct Attack Munition (JDAM). If the Iranian project proves similarly successful, Israel’s enemies will achieve the capability of striking within five to 10 yards of their intended targets.

Converting an unguided rocket (what some Israeli military types call “statistical” rockets) into a precision-guided munition is both simple and complicated. It’s simple because all it takes are tail fins, a circuit board, and the right software. One former Israeli official estimates that an entire PGM-making kit might cost as little as $15,000 per munition. But it’s also complicated because dismantling a rocket to retrofit it with precision-guided technology and then reassembling it requires knowledge and infrastructure that Iran’s low-tech proxies don’t have. They are laboring to acquire them. But with the Israelis patrolling from the skies with remarkably accurate intelligence, the tasks of transporting parts and assembling PGMs have become hazardous. Israel’s estimated 300 strikes in recent years have reduced the PGM talent pool and destroyed a significant amount of hardware.

Iran and Israel have been playing a quiet game of chess across the Middle East—difficult for the casual observer to discern but punctuated by the periodic explosion. The Iranian effort continues despite the occasional setbacks. And so does the Israeli effort, which is thankless and time-intensive. Both sides understand that when enough PGMs reach the hands of Israel’s enemies, the effect will indeed be game-changing.

First, PGMs will force Israel to use far more Iron Dome interceptors than it currently deploys. The cost of each ranges roughly from $50,000 to $100,000. Thus, defending Israel could soon become much more expensive. If Israel had been forced to shoot down all 450 PIJ rocket volleys with Iron Dome in November, the cost would have been as much as $45 million.

More worrying, with enough PGMs fired at the same target, Iran’s proxies may be able to outmaneuver, outsmart, or overwhelm Israeli missile-defense systems, with the result that one or more rockets would get through. Hamas already claims to be able to do this with its unguided rockets. Such claims are dubious now. But in the future, if the intended target is the chemical plant in Haifa, the Kiriya (Israel’s defense headquarters) in Tel Aviv, Ben Gurion International Airport, or a Tel Aviv office building, the results could be catastrophic. As Prime Minister Benjamin Netanyahu’s former national-security adviser Jacob Nagel recently told me, “with enough PGMs, the impact on certain targets could be close to the impact of a nuclear weapon.” He adds that, for this reason, “after the Iranian nuclear threat, Israeli leaders cite the PGM threat as next on their list.”

Currently, the Israelis believe that the Lebanese terrorist organization Hezbollah is the only Iranian proxy group that possesses Iranian PGMs in any significant number. The Israelis are not saying how many Hezbollah has. But they acknowledge that the efforts to interdict PGMs or PGM parts have not completely prevented the technology from reaching Iran’s Lebanese surrogate. And Hezbollah continues to work feverishly on this project.

Netanyahu also recently indicated that the Iranian proxy in Yemen, the Houthis, may also have PGMs. So far, the Houthis have targeted only Saudi Arabia with simple rockets, cruise missiles, and drones. Netanyahu’s warning implies that the group may one day target Israel with long-range PGMs at Iran’s urging.

Of course, the Iranians have their own arsenal of PGMs—more formidable ones. They are not retrofitted but rather built from scratch. And some of them are even immune to GPS-jamming systems, which is one of the best countermeasures Israel has against these munitions.

Israel’s military brass would much rather destroy PGMs on the ground than intercept them in the air. One problem they have is patrolling the vast territory Iran controls to build, store, and launch its munitions.

Iran has, for the past five years, been building a land bridge extending across the Levant. The ultimate goal is to establish hegemony across the region. But the short-term goal is far more attainable: to control, via proxy, territory stretching from western Iran through Iraq, into Syria, through Lebanon, and all the way to Israel’s doorstep. In addition to deploying Hezbollah in Lebanon, Iran is using the Assad regime in Syria and Shiite militias in Iraq to maintain this real estate. Some question whether these proxies would dare fire on Israel with PGMs. The Israelis have answered that question, in part, with those punishing air strikes on Iranian assets in Iraq and Syria.

Critics assert that Netanyahu has cynically used such strikes as a means to campaign as the tougher defense candidate during Israel’s unprecedented two rounds of stalemated elections in 2019. But Israeli strikes in Iraq and Syria were not optional in the eyes of the country’s military planners. Iranian PGMs, or at least PGM parts or infrastructure, were thought to be there.

Targeting precision-guided munitions will become even more complicated in the future. The regime in Iran is not only working assiduously to obscure their transport and assembly. It is also devising ways to store them under homes, schools, hospitals, apartment buildings, refugee camps, and other heavily populated civilian infrastructure. Israel has already dealt with this problem in Gaza. Hamas conducts military operations from within civilian population centers. The Israelis warn that it will be worse in Lebanon, with Hezbollah’s arsenal already strategically embedded in civilian areas. PGMs of an unknown quantity will be among these caches. The decision to strike these weapons on the ground will be excruciating for the IDF. And every strike will create immense public-relations damage, as images of injured or dead civilians fill the television screens and Twitter feeds of news consumers worldwide.

Of course, Israel is not the only country forced to deal with this problem. The United States has encountered human shields on the battlefields of Iraq and Afghanistan, too. The prevalence of the problem prompted President Donald Trump to sign into law the “Sanctioning the Use of Civilians as Defenseless Shields Act.” The bill passed unanimously in both the House and Senate before reaching the president’s desk in December 2018. A variant of the bill is also circulating at the United Nations.

These measures are important for two reasons. First, when those complicit in building the human-shields infrastructure (tunnels, bunkers, and storage facilities, for example) know they can be sanctioned by the U.S. government or even the UN, they may be less inclined to contribute to this cynical project. Being named can have an immediate impact among the local population, which (with a few exceptions) would not appreciate being treated like cannon fodder.

More important, these measures can enhance the operational legitimacy and freedom of the Israel Defense Force in future conflicts. Once it has been established that targeting human-shields infrastructure is legal and protected from international opprobrium (to some extent), Israel’s enemies lose one of their key advantages.

Unfortunately for Israel, no amount of inspired legislation will stop Hezbollah or Iran’s other proxy groups from pursuing this precision project. If anything, when the Iranian PGM project comes online, the only significant disruption to the status quo will be inside Israel.

With PGMs, the era of Iron Dome’s total dominance may come to an end. This does not mean that the Israelis will stop using this remarkable system to protect its citizens from incoming rockets. But barring significant improvements to counter PGMs, Iron Dome may no longer provide the Israeli leadership with the luxury of time to weigh their options when they must respond to a hailstorm of precision strikes.

Should PGMs pierce Israel’s defenses and hit more of the intended targets, the Israeli public will demand a response. The political and military leadership will be forced to respond more rapidly and with greater force. This will increase the odds of mistakes on the battlefield and thus the odds of escalation. And if PGMs are fired from multiple locations, the natural result will be a multifront war.

If Israel doesn’t find a way to halt Iran’s PGM project, the very character of its wars will change. Despite a steady stream of attacks perpetrated by their enemies in recent years, the Israelis have not needed to fight long or particularly bloody wars. Instead, they have been conducting limited operations. Israel has, in fact, often been able to determine the beginning and end of these flare-ups. Iron Dome’s ability to neutralize rudimentary rockets has made that possible. But now, with PGMs in play, Israel may no longer be able to dictate the terms of conflict when its enemies want one.

And let there be no doubt: They want one.