Russian forces have begun using Iranian-made drones in attacks on Ukrainian forces.
Moscow appears to be using the drones to compensate for shortfalls in artillery and airpower.
Experts say the drones have limited utility but it's unclear what impact they'll have on the battlefield.
With Russia's invasion of Ukraine faltering, Moscow has turned to an unlikely savior: Iran.
Russian forces in Ukraine are using Iranian-made "kamikaze" drones that have already destroyed precious Ukrainian artillery around Kharkiv, where Kyiv launched a successful counterattack that has driven back Russian troops.
Iranian-made Shahed-136 drones appear to be compensating for Russian airpower that has proven ineffective in combat and for Russian artillery that has concentrated far to the south of Kharkiv.
"In other areas, the Russians have overwhelming artillery firepower, and they manage with that," a Ukrainian colonel in the Kharkiv region told The Wall Street Journal. "Here, they no longer have that artillery advantage, and so they have started to resort to these drones."
Aside from the initial shock of encountering Iranian drones 1,200 miles from Tehran, it's not clear what impact the drones will have on the battlefield.
"I think we are at the early stages of assessing their usability," Samuel Bendett, an expert on Russian drones at the Center for Naval Analyses, told Insider. "They can hit Ukrainian long-range artillery - highly prized Russian targets - as well stationary targets like buildings."
Ironically, it was Ukraine that initially reaped the advantage of UAVs: Its Turkish-made TB2 Bayraktar attack drones, armed with laser-guided anti-tank missiles, took a surprising toll of Russian armor in the early days of the war.
But the TB-2 is a somewhat large, clumsy drone with a 39-foot wingspan and a maximum speed of just 137 mph.
Iran's Shahed-136, and its smaller cousin, the Shahed-131, which Russia is also using, are loitering munitions that are a cross between a drone and a missile: With a camera in their nose, they orbit a target like a drone until an operator on the ground smashes them into tanks, howitzers, and bunkers just like a missile.
The delta-winged Shahed-136 has a wingspan of about 8 feet and a cruising speed of about 112 mph, according to the Ukrainian military. Iran claims the UAV has a remarkable range of more than 1,550 miles, which would make it bigger and faster than the backpack-carried Switchblade kamikaze drones that the US has supplied to Ukraine.
Western analysts were quick to point out the Shahed-136's flaws.
Justin Bronk, an airpower expert at Britain's Royal United Services Institute think tank, noted several limitations of bargain-basement kamikaze drones: commercial GPS guidance that's jammable, small warheads of less than 50 pounds, commercial components vulnerable to anti-drone microwave weapons, and difficulty hitting moving targets.
For Ukraine, perhaps the best news is that the Shahed-136 isn't hard to shoot down.
"They are slow- and low-flying, which significantly limits their utility as responsive weapons against a sudden threat at range and also makes them comparatively easy to intercept with old-fashioned radar-laid anti-aircraft guns," Bronk wrote, pointing to Germany's Gepard self-propelled anti-aircraft gun, which Berlin has supplied to Kyiv.
But loitering munitions like the Shahed-136 are fairly cheap and easy to operate, which could enable Russia to employ swarm tactics that overwhelm a target with hordes of drones.
"Russia's Shahed-136s are certainly an increasing problem for Ukraine," Bronk concluded. "Air defenses cannot intercept them all, and they will cause damage to cities, bases and probably SAM radars. Western partners should increase deliveries of short- and medium-range air defenses to help."
This suggests an emerging contest between Ukrainian air defenses and large numbers of Iranian-made kamikaze drones. "I think a lot will depend on whether Russian military can field them in large enough numbers to begin overwhelming Ukrainian air defenses," Bendett said.
One embarrassing question is why Russia - which has invested heavily in drones - can't field its own cheap loitering munitions. Another is whether Iran will continue to supply Russia with large numbers of drones.
Like Turkey, Iran has emerged as a major player in the world of drones, which are relatively easy for smaller countries to develop and acquire compared to weapons like jets and tanks. Iranian-made drones have been used in attacks on Saudi oil fields, and Tehran has sold them to Venezuela.
Russia and Iran have been in a marriage of convenience for years - in part to spite the US - with Iran buying Russian weapons like the S-300 anti-aircraft system, and Tehran may see support for Moscow now as another way to counter the US.
But Ukraine downgraded its relations with Iran over the drone sales, and with Tehran still facing heavy international sanctions and buffeted by increasing domestic unrest, picking a fight over Ukraine seems risky. Then again, Russia and Iran, already pariahs, may feel they have nothing to lose.
Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds a master's in political science. Follow him on Twitter and LinkedIn.