The Russian military is getting better at taking down enemy drones. That could have serious implications for the United States as it relies more on unmanned aircraft.

The crews of Silok electronic-warfare vehicles "forced to land unmanned aerial vehicles" during a war game near Leningrad involving 500 service members, the Kremlin announced on Nov. 2.

Silok is the latest in a long line of radio-frequency-jamming systems that the Russian military has deployed since the Cold War in order to block enemy communications, including the radio links that allow the operators to control drones -- and drones to send back video and other intelligence data.

In the war game, "unidentified UAVs of various modifications attempted to intrude into the closed flight airspace," the Kremlin stated. "The servicemen used Silok equipment to locate [the] air intruders and forced them to land.

"Afterwards, engineering and sapper units defused improvised explosive devices mounted on the UAVs, and military-police rapid-response teams detained operators who controlled them."

While the Russian army, and the Soviet army before it, long has operated R.F.-jammers, it wasn't until October 2017 that the Kremlin stood up its first ground-based unit specializing in defeating enemy drones.

The Russians also deployed R.F.-jammers to Syria to protect Moscow's installations in that country. The new Silok jammer joined the Russian force in Syria in August 2018.

The drone threat is acute in Syria. On the night of Jan. 5, 2018, a swarm of explosives-laden small unmanned aerial vehicles, apparently controlled by Syrian rebels, attacked two Russian bases in western Syria.

Ten of the drones, which the Kremlin described as "aircraft-type," assaulted Khmeimim air base, where Russia stages most of its air power in Syria. Meanwhile, three drones attacked Russian facilities at the nearby port of Tartus. Russia intervened in the Syrian civil war on the side of the Syrian regime starting in late 2015.

Each of the drones carried 10 one-pound bombs under its wings, the Kremlin claimed.

A Pantsir-S air-defense system shot down seven of the drones while Russian electronic-warfare specialists forced six of the UAVs to land, presumably by jamming their radio control links.

The proliferation of jammers and Russia's growing prowess in using them could threaten the U.S. military's expanding fleet of UAVs. In 2011, Iran apparently used a Russian-made Avtobaza jammer to force down a U.S. Air Force RQ-170 stealth spy drone along the Afghanistan-Iran border. Russia reportedly jammed American UAVs over Ukraine in 2014.

The Pentagon is keenly aware of the risk. The Defense Advanced Research Projects Agency's (DARPA) long-running Communications Under Extreme R.F. Spectrum Conditions initiative and similar programs aim to develop "signal detection and reasoning technology that allows radios to recognize interference and jamming, and adapt to maintain communications — even in the presence of severe and/or adaptive jamming," according to DARPA program manager Joseph Evans.

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DARPA's effort focuses on radio systems that can better detect and assess jamming, change their frequencies and process degraded data to make sense of it.

In parallel, the U.S. Air Force is working on algorithms that could allow a drone to process its own sensor data -- and, for example, identify targets -- before relaying them via radio to an operator on the ground. "Processing and exploitation is going to happen on the sensor — it’s not going to happen in a centralized hub on a landmass somewhere," Lt. Gen. VeraLinn Jamieson, an Air Force deputy chief of staff, said in August 2018.

The less information a drone must relay, the less vulnerable it is to jamming.

Likewise, the more a UAV can launch, navigate and land on its own, the less it needs a strong radio link to its operator. In September 2018 an Air Force Reaper drone completed the first successful autonomous landing for the type.

Thanks to better sensors and software, U.S. drones steadily are becoming more autonomous. But they'll always need some kind of radio link in order to send back sensor data and other intelligence. That's one weakness Russia could continue to exploit.