The proliferation of cheap, deadly uncrewed aerial vehicles (UAVs) into conflicts around the world has presented a new challenge for military leaders.
While modern air defences are designed to effectively target limited numbers of large, highly-capable fighter and bomber aircraft using costly precision missiles, such systems are proving unsuitable for protecting friendly airspace against large quantities of small suicide drones – formally known as one-way UAVs.
These small vehicles fly low and slow, and cost just a fraction of what a high-end anti-air missile does. Attempting to target waves of one-way UAVs with conventional air defences would quickly exhaust the limited supply of munitions.
Russia and Ukraine have fired dozens of such weapons at one another during individual attacks.
Compounding the problem is how low such vehicles fly – as little as 200ft above ground level, according to the European headquarters of the US Air Force.
At such minuscule heights, the curvature of the Earth makes it so that conventional air defence radars can only track objects at a distance of around 10nm (18.5km), according to General James Hecker, the commander of US Air Forces in Europe.
Speaking at the 2024 Air & Space Forces Association conference near Washington, DC on 17 September, Hecker explained the challenge posed by the new weapon systems – and how Ukraine is defending against them.
“You have to see them first with a ground system,” he explains, noting the detection issues with radar, and the cost of each station, make that option impractical.
“It’s a very difficult problem,” Hecker says. “The one-way UAV threat is very new.”
Once ground systems identify the target, interceptor aircraft or air defence systems can be tasked with identifying and destroying the threat. This often occurs at night, posing additional challenges for manned fighters or ground operators.
Ukraine’s solution to this problem is a novel approach that targets the acoustic signature of incoming aerial threats.
Kyiv has deployed a system called Sky Fortress throughout the country to detect and triangulate one-way UAVs by listening for them. Hecker says the network deployed in Ukraine includes 9,500 ground-based microphones that match sounds in the environment to known audio signatures of aerial vehicles.
Once threats have been identified, more affordable defences can be deployed against the slow moving drones, such as man-portable air defence missiles like the FIM-92 Stinger or anti-aircraft batteries like the German Gepard system.
“This is a cheap solution,” Hecker says, praising the Sky Fortress concept’s ability to get on the “right side of the cost curve”.
Two Ukrainian engineers conceived and developed the acoustic detection system, with the first version essentially consisting of mobile phones mounted on 2m poles. Each of those sensor stations only cost around $300, according to Hecker.
Subsequent improvements have raised the price slightly, but it remains a highly affordable option for defending against slow, low-flying swarms of UAVs. Hecker estimates a country like Romania, which sits across the Black Sea from Russia, could be fully networked with such a detection system for a cost of around $6 million.
Earlier this month Bucharest reported that Russian drones breached the country’s airspace, with Romanian F-16s scrambled to intercept the incursion – a prime example of the cost imbalance problem posed by one-way UAVs.
Although NATO has stepped up its air-policing efforts along the alliance’s eastern flank, Hecker says there simply are not enough fighters and air defence batteries to actively monitor the entire region.
“We don’t have enough assets to just line the entire border we have with Russia and NATO,” the Boeing F-15C and Lockheed Martin F-22 pilot says.
The low price point and effectiveness of the Sky Fortress system is attracting attention within the alliance. Hecker says NATO has arranged demonstrations of the technology in Germany and Romania, with representatives of multiple members states attending.
“I think its getting a lot of interest,” Hecker says.
The four-star general notes he mentioned Sky Fortress to the defence minister of Latvia, after that NATO member’s airspace was also breached by Russian drones earlier this month.
Hecker says the latest version of Sky Fortress can detect threats as high as 10,000ft above ground level.
