The Russian military received its first shipments of Iranian-made drones to assist on the battlefield in its invasion of Ukraine, but in tests of the systems before they were deployed, the drones failed preliminary operational tests, the Washington Post reports.

Russia accepted an unknown number of Shahed-129, Shahed-191 and Mohajer-6 drones from Iran, who have also supplied them to extremist groups in Yemen, Iraq and Syria.  However, the drones–which can be used to lurk over an area for observation or to deploy weapons–have not faced sophisticated defense systems like they would see in Ukraine.  Iran’s surrogate groups have used the drones in swarm attacks on opposition positions, including one that hit a US position in Syria last week.

“These Iranian drones have not operated in a sophisticated air-defense environment before,” Michael Knights, a military and security expert with the Washington Institute for Near East Policy, said. “The closest they’ve come to that is with [Houthi strikes against] Saudi Arabia or against U.S. bases in Iraq, and they have generally not done well. So I wouldn’t be surprised that, in a more intense environment like Ukraine, that they would have some problems.”

In field tests, the Russians found the Iranian drones malfunctioned, wandering off course for extended periods that made them ineffective when targeting specific objectives.  The drones would also frequently fail to launch.

Analysts believe the Russians sought the drones because their fleet of drones are geared for surveillance.  Russia has two nations, China and Iran, which are still trading with it that can supply it with drones, but China is an unwilling partner because it fears retaliation from the US and its Western allies.