WASHINGTON • Kurdish forces fighting the Islamic State in Iraq and Syria (ISIS) group in northern Iraq last week shot down a small drone the size of a model airplane.
They believed it was like the dozens of drones that the terrorist organisation has been flying for reconnaissance in the area, and they transported it back to their outpost.
But as they were taking it apart it blew up, killing two Kurdish fighters in what is believed to be one of the first times that ISIS has successfully used a drone with explosives to kill troops on the battlefield.
Over the past month, ISIS has tried at least twice to use small drones to launch attacks, prompting US commanders in Iraq to warn forces fighting the group to treat any type of small flying craft as a potential explosive device.
ISIS has been using surveillance drones on the battlefield for some time, but the attacks - all targeting Iraqi troops - have highlighted its success in adapting readily accessible technology into a potentially effective new weapon. US advisers have warned that ISIS could deploy drones against coalition forces in the battle in Mosul.
KNOW THE ENEMY
This is an enemy that learns as it goes along. ''
LIEUTENANT-GENERAL SEAN MACFARLAND
For some US military analysts and drone experts, the episodes confirmed their view that the Pentagon - which is still struggling to come up with ways to bring down drones - was slow to anticipate that militants would turn drones into weapons.
"We should have been ready for this, and we weren't," said Mr P. W. Singer, a specialist on robotic weaponry at New America, a think-tank in Washington.
Military officials said that the Pentagon had dedicated significant resources to stopping drones but that few Iraqi and Kurdish units had been provided with the sophisticated devices that US troops use to disarm them.
The officials said they had ordered the Pentagon agency in charge of dealing with explosive devices - known as the Joint Improvised-Threat Defeat Organisation - to study ways to thwart hostile drones. The Pentagon has requested US$20 million (S$27.6 million) from Congress for this effort.
In recent months, the Central Intelligence Agency and the Defence Intelligence Agency both rushed to complete classified assessments about ISIS' drone use. And the Secretary of the Army, Mr Eric Fanning, recently assigned a special office to respond to emerging threats and to study how to stop drones.
Unlike the US military, which flies drones as large as small passenger planes that need to take off and land on a runway, ISIS is using simpler, commercially available drones such as the DJI Phantom, which can be bought on Amazon. The group attaches small explosive devices to them, essentially making them remotely piloted bombs.
"This is an enemy that learns as it goes along," said Lieutenant-General Sean MacFarland, the top US military commander in Iraq until August.
Of the three known drone attacks in Iraq, only the one involving the Kurdish soldiers caused casualties.
"The explosive device inside was disguised as a battery - there was a very small amount of explosives in it, but it was enough to go off and kill them," said a senior US official.