The United States is sending American troops to the Middle East to provide better air and missile defenses after an aerial attack on Saudi oil targets last week. The raid began around 4 a.m. on the morning of Sept. 14, with explosions rippling across the Kurais and Abqaiq Aramco oil processing facilities inside Saudi Arabia as the sound of defensive automatic machine-gun fire rang in the air.

After the fall of the Soviet Union, the U.S. Army sharply downsized its short-range anti-air capabilities in the belief that they were no longer greatly needed.

In theory, the oil facilities both lay under the defensive umbrella of Patriot PAC-2 surface-to-air missile batteries that the U.S. sold to Saudi Arabia to intercept aircraft and missiles up to 100 miles away. However, if Saudi radars detected the 18 triangular drones and seven cruise missiles (judging by recovered debris) that bombarded them last week, they did so too late. Instead, they were forced to fire sporadically with automatic weapons, which didn’t prevent widespread damage that temporarily disrupted shipments of 5.7 million barrels of oil daily — half of Saudi Arabia’s output.

Indeed, while the U.S. troops are intended to provide help against this type of threat — believed to have been launched by Iran — air attacks by low-flying drones and cruise missiles are exactly the types of systems the U.S. is having trouble defending against after years of focusing on longer-range threats.

Short-range air defense systems — or SHORADS in Army lingo — have existed almost as long as combat aircraft, and are used to protect vital bases and facilities, as well as troops on the front lines. In both the world wars, they consisted of heavy machine guns and rapid-fire cannons designed to rake warplanes as they swooped down to attack. During the Cold War, anti-aircraft artillery increasingly benefited from radar guidance, and were joined by heat-seeking missiles fired by vehicles or bazooka-like shoulder launchers.

However, after the fall of the Soviet Union, the U.S. Army sharply downsized its short-range anti-air capabilities in the belief that they were no longer greatly needed. They trusted that U.S. jet fighters could neutralize most enemy aircraft before they became a problem. Two threats that have grown significantly these days — drones and ground skimming cruise missiles — were minimal at that point: Armed drones were rare and expensive, and the Soviet Union was the only adversary that had many land-attack cruise missiles and it wasn’t expected that other countries, let alone terrorist groups, would develop them.

Instead, the Pentagon saw a need for medium- and long-range air defenses like the Patriot to protect against ballistic missiles that arc high up into the exo-atmosphere at immense speeds and long distances. That’s where they focused the military’s planning — to some success, as suggested by the Saudi-based Patriot battery’s record of intercepting dozens of high-flying ballistic missiles from Yemen in recent years.

But it turned out that the threat that has grown most rapidly in recent years comes not from manned aircraft, but the drones and low-flying cruise missiles that are proliferating rapidly across the globe due to exports from China, Israel and Russia.

Drones and missiles can be detected by radar, but they tend to have small radar signatures and can fly close to the ground, sharply reducing the detection range and thus opportunities to fire on them from far away. They also are easy to maneuver, allowing them to hit the coverage gaps between radars and Patriot batteries. And drones and cruise missiles are often cheaper than a $2 million or $3 million Patriot missile, meaning the supply of Patriots can be depleted much faster than the bevy of drones launching attacks.

That’s why short-range defenses that protect against targets within visual range are so important: Some targets aren’t likely to be consistently detected from far away, and long-range missiles are too expensive to use against certain cheap but numerous threats.

Even organizations like ISIS have cobbled together surveillance and combat drones. During the battle to liberate the Iraqi metropolis of Mosul in 2016-17, ISIS made extensive use of small grenade-bearing drones against Iraqi and U.S. troops.

There are some existing systems to handle these threats, but most rely on Cold War-era technology designed to shoot down airplanes and helicopters. The Saudi Abqaiq oil facility was guarded by a half-dozen Shahine short-range missile systems and radar-guided air defense cannons, but since neither of the old systems were designed for defense against drones or missiles, they did very little good.

To its credit, the U.S. Army has realized the dangerous new vulnerability and in the last few years has made deploying more SHORAD capabilities one of its six top modernization priorities. Among other ideas in development, by 2022 the Army will field a specialized wheeled armored vehicle with a missile-armed turret as well as a cannon specifically for providing air defenses that accompany troops moving forward in battle.

In the meantime, to fulfill a congressional mandate to obtain a stop-gap defense system against cruise missiles, the Pentagon announced plans in 2019 to take the rare step of purchasing arms not entirely American-made. The military purchased two batteries of the Iron Dome air defense system Israel developed with help from the U.S. to shoot down unguided rockets fired by Palestinian militants. However, the missiles used as interceptors still cost around $40,000 dollars each, while commercial drones may cost considerably less. Thus drones could potentially overwhelm existing defenses with sheer numbers.

Another option in development — by China and Russia as well as the United States — is the use of laser weapons that could burn drones or missiles out of the sky with a “shot” that costs virtually nothing (though the weapons themselves aren’t cheap). Lasers also boast very fast reaction times and a high degree of accuracy. On the downside, lasers lack a kinetic “punch” to jar an incoming missile off its trajectory if the laser’s heat doesn’t do the job; they can be degraded by foggy conditions; and they require a lot of power to work at longer distances.

Short-range air defenses are not a magic bullet — and in fact work best when integrated with longer-range defenses.

Deploying more electronic warfare systems that can disrupt or even hijack the communications links between drones and their operators is another approach that has proven successful when tested in combat by Russia and the United States. Recently, U.S. Marines used a jeep-mounted jammer on the deck of a carrier to bring down an Iranian drone.

Short-range air defenses are not a magic bullet — and in fact work best when integrated with longer-range defenses. They can be overwhelmed or picked off by more advanced weapons, and may easily end up far more expensive than threats they are designed to counter. Furthermore, by their nature, short-range defenses cannot provide blanket protection for a region but must be deployed selectively to protect key facilities and vulnerable front-line combat units.

But even if there’s no such thing as a perfect defense, deploying new short-range air defenses will remain vital in the 21st century — not only to protect the lives of soldiers on the front lines or valuable military bases, but also to defend vital civilian infrastructure, as the recent attack on Saudi Arabia’s oil processing facilities vividly demonstrates.