This article originally appeared in Popular Science.
To confuse Russian aircraft, Ukraine reportedly has access to a training tool from the United States. Known as “Threat Emitters,” they are a way for pilots to learn the signatures of hostile aircraft and missiles, allowing them to safely practice identifying and reacting to combat situations in training. In simulated scenarios, pilots learn how their sensors would perceive real threats, and can safely plan and adapt to the various anti-aircraft weapons they might encounter. The net effect is that pilots learn to fight against a phantom representation of air defenses, in preparation for the real thing.
But when brought to actual war, the emitters in turn are a way to make an enemy’s sensors less reliable, confounding adversarial pilots about what is real and what is merely an electromagnetic mirage.
These “low-cost emitters were built for ranges inside the U.S. but now are in the hands of Ukrainians,” reported Aviation Week, citing Air Force Chief of Staff Charles Q. Brown Jr. “The emitters can replicate surface-to-air missiles and aircraft, and are a cheap, innovative way to further complicate the air picture for Russia.”
One such system is the Joint Threat Emitter. There are two major components to the system: a command unit that lets soldiers operate it, and trailer-mounted radar threat emitters. A command unit can control up to 12 different threat emitters, and each emitter can simulate up to six threats at once.
These emitters help pilots train on their sensors, practicing for war when far from conflict. In 2013, the Air Force and Navy set up Joint Threat Emitters at Andersen Air Force Base on Guam. Both the Navy and Air Force operate from the island, and as the American territory closest to North Korea and China, Guam is prominently featured in war plans around either country.
“When [pilots] go to a real-world situation, they won’t see anything that we haven’t thrown at them before,” Staff Sgt. Rick Woltkamp, a ground radar systems craftsman with the Idaho Air National Guard, said in 2013. “We simulate a ground attack, and the pilot will react and respond accordingly to the simulation.”
Development and use of the tech goes back two decades. In 2002, the Air Force selected Northrop Grumman to develop the Joint Threat Emitter over the next 10 years as a “high-fidelity, full-power threat simulator that is capable of generating radar signals associated with threat systems” that will “better enable aircrews to train in modern war environments.”
Some of the signals it can generate mimic surface-to-air missiles and anti-aircraft artillery, both of which threaten planes but require different countermeasures. One example of a non-missile air defense system is the ZSU-23, built by the Soviet Union. The ZSU is an armored vehicle with anti-aircraft guns pointed on a turret that uses a radar dish to guide its targeting. As a Soviet-made system, ZSU-23 systems were handed down to successor states, and are reportedly in operation by both the militaries of Ukraine and Russia.
When used for training purposes, the Joint Threat Emitters let pilots perceive and adapt to the presence of enemies, beyond visual line of sight. At these distances, pilots rely largely on sensor readings to see and anticipate the danger they are flying into. One way for them to adapt might be to pick a new route, further from the anti-air radars. Another would be to divert the attack to knock out anti-air systems first.
In Ukraine, the likely use case for these emitters is to augment the country’s existing air defenses. Using the emitters to project air-defense signals across the battlefield—signals identical to known and real Ukrainian air defenses—could mask where the actual defenses are. Real defenses lurking in a sea of mirage defenses, simulated but not backed up by the actual weapons, is a vexing proposition for an attacker. Discovering what is real means probing the defenses with scouts (or hoping that satellite imagery provides a timely update). But because the emitters, like the weapons they emulate, can be driven around, even a view from space cannot accurately pin down a fixed location for long.
Russia’s air force has struggled to achieve air superiority over Ukraine since it invaded in February 2022. Existing air defenses, from vintage human-portable missiles to newer arrivals, put planes and helicopters at real risk for attack. Videos of Russian helicopters lobbing rockets, increasing range while greatly reducing accuracy, suggest that even in the war’s earliest months Russian pilots were afraid of existing Ukrainian anti-air defenses.
While the threat emitters alone do not offer any direct way to shoot down aircraft, having them in place makes Russia’s work of attacking from the sky that much harder. Even if a threat emitter is found and destroyed, it likely means that Russia spent ammunition hitting a decoy target, while missing a real and tangible threat.