On July 19, Ukraine’s 58th Separate Motorized Infantry Brigade destroyed two bridges in Russia’s Belgorod region in a brazen raid that revealed just how potent low-cost first-person-view drones are in war. The attack, in which the brigade used a pair of inexpensive FPV drones to take out the two bridges near the border with Ukraine’s Kharkiv region, not only delivered a potentially embarrassing blow to Russia. It also offered a powerful example of the kind of innovation Ukraine needs to keep fighting under increasingly difficult circumstances.

Footage shared by the brigade shows one of the drones flying in for the kill after it had identified Russian mines and ammunition hidden under the bridge. It detonates at the top of the video in a cloud of smoke as another camera filming from a distance captures the explosion.

Both bridges, according to the Ukrainian unit, had been mined by the Russian military and were being used as supply routes for troops operating near the frontline in Kharkiv. The Russian military was apparently preparing to blow up the bridges if it found itself in need of a hasty retreat, according to the 58th Brigade.

“The warehouses were built under the bridges. They (Russians) were leaving the ammunition there and guarding it,” the brigade’s representative said. “It became clear that something was going on there.”

The Brigade first noticed unusual activity at one of the two bridges and suspected a Russian ammunition depot. Standard reconnaissance drones were unable to fly directly beneath the structure, however, without losing signal. So the brigade turned to a larger, FPV-equipped drone fitted with fiber optics to inspect the area below.

Once it had arrived at the bridge, the drone discovered anti-tank mines and other ammunition concealed beneath the bridge. “We saw the mines, and we struck,” the brigade representative said in a statement.

CNN geolocated the bridge to Russia’s Belgorod region, just across the border from Ukraine’s Kharkiv region. The unit checked another bridge in the area and confirmed that it, too, was mined. It then launched another drone at the structure, which also exploded.

“After the first success, we saw an opportunity and took it,” the brigade said. Ukraine’s SBU state security service previously claimed to have captured a Russian soldier who worked at the ammunition depot under the bridge, accusing him of negligence in its handling of intelligence materials and weapons.

The inexpensive drones Ukraine used to destroy the two bridges are typically used by hobbyists. In many cases, the kits for them can be purchased in local stores for 25,000 to 30,000 Ukrainian hryvnias, or roughly $600–$725. In comparison, Ukraine’s HIMARS rocket systems, also used for taking out Russian infrastructure, cost millions of dollars per launcher, while individual rockets can run into the tens of thousands.

The cheap drones have already proven potent on the battlefield, with Ukraine using FPV drones to target Russian military airfields in June. Small drones were smuggled in close to Russia’s airfields to attack, with hundreds of aircraft damaged or destroyed at seven different locations.

Drones have become an increasingly critical component of Ukraine’s defense as the war has evolved. With Russian forces grinding their way forward in eastern Ukraine, Kyiv’s troops have found themselves in desperate need of alternatives to holding the line as Western support sometimes falters. FPV drones, which are easy to make and fly using commercial off-the-shelf parts and open-source designs, are one of the most effective tools available.

“This new technology, some of it only created by Ukrainians, can be modified and put in the hands of trained personnel almost immediately to get real results on the battlefield,” Mykola Bielieskov, a military analyst, said.

“I believe these types of operations show how even modest technology can achieve outsized results if used creatively.” That innovation is more important now than ever before. Moscow has pledged to step up its near-daily missile and drone strikes on Ukrainian cities. In an interview earlier in July, Putin said he was not interested in agreeing to a ceasefire until Russia’s forces have finished their offensive.

If Ukrainian forces can use drones to fight back at will in Russia itself, its ability to stave off Russian advances may only grow. So far, Russia has not responded publicly to the destroyed bridges in Belgorod. The loss of two supply lines in its Belgorod region, however, could have a major impact on Russia’s logistics in the region.