US Tries Israeli 'Roof Knock' Airstrike Tactic to Avoid Killing Civilians — But It Doesn't Work

The US military said that it is using "roof knock" strikes in Iraq and Syria in order to try to compel civilians to flee from buildings that will be targeted by US military and other coalition aircraft — a controversial tactic that the US has borrowed from Israel, which used it during the 2014 Gaza conflict.

Major General Peter Gerstner, deputy commander for the anti-Islamic State Operation Inherent Resolve, said that in one case "about four weeks ago," the US military detonated a Hellfire missile above a house in Mosul in an effort to warn a woman and children previously seen coming and going from the building of an impending attack.

'We went as far as actually to put a Hellfire on top of the building and air burst it so it wouldn't destroy the building, simply knock on the roof to ensure that she and the children were out of the building,' Gerstner told a Pentagon press conference Tuesday. "And then we proceeded with our operations."

Gerstner said the woman then left the house — which he said was housing an Islamic State finance chief and $150 million in cash — along with a number of Islamic State fighters. But then the woman went back in after the second, more destructive bomb had already been launched from the aircraft.

"So, as much as we tried to do exactly what we wanted to do and minimize civilian casualties, post-weapons release, she actually ran back into the building," he said. "That's a — we watched, very difficult for us to watch. And it was within the final seconds of the actual impact."

Gerstner said he could not be certain if the Islamic State militant targeted in the airstrike was killed.

The announcement came a week after the US military said that the number of civilians killed by US-led coalition airstrikes in the nearly two year-old war against IS had increased to 41 people. Human rights groups say the number is likely much higher, with the watchdog organization Air Wars estimating the number to more likely be around 1,200 civilians.

The roof knock is a well-known and controversial tactic used by the Israeli military to both minimize civilian casualties and to absolve the chain of command of accusations of violating the Geneva Conventions by disproportionately killing civilians in populated areas.

In the Israeli technique, a bomb that contains little or no explosive is shot at a house to warn inhabitants that the structure is about to be destroyed by a much larger munition.

The tactic was used most notably in Gaza two years ago, when the Israeli military combined the roof knock with dropping leaflets and text messages and calls directly to civilian cell phones to warn residents of an impending attack.

Numerous incidents of the roof knocks were filmed during the Gaza conflict. The UN found that 1,462 civilians were killed in that war, more than half of them in residential buildings hit by Israeli airstrikes.

In this video depicting an Israeli "roof knock" airstrike in Gaza in 2014, the man in the background says, "Warning bomb, warning bomb."

Another "roof knock" airstrike by Israel's air force in Gaza in 2014.

Human rights groups and the UN commission tasked with investigating the war determined that the roof knock technique was not an effective tactic to avoid civilian casualties.

"There is no way that firing a missile at a civilian home can constitute an effective 'warning,'" Philip Luther, director of the Middle East and North Africa program at Amnesty International, wrote in a report on the 2014 conflict.

The UN report said civilians were often confused as to what to do after hearing the first bomb go off.

"In a number of incidents examined, the concerned persons either did not understand that their house had been the subject of a "roof-knock", or the time given for evacuation between the warning and the actual strike was insufficient," the UN report said.

The report highlighted the death of 19 people from one family who the UN said were given only a few minutes to evacuate in the early hours of the morning after a roof-knock strike woke them up.

The UN also faulted the Israelis for failing to re-examine the effectiveness of roof knock warnings as the civilian toll continued to mount.

"The limited effectiveness of the above-mentioned precautionary measures must have become abundantly clear in the early days of the operation, given that many buildings were destroyed, together with their inhabitants."

US Air Force General Gerstner said the US military did not receive any training from the Israelis on the use of the roof knock method, and said it was just one of several ways commanders were trying to minimize civilian casualties.

Air Wars Director Chris Woods said that while he appreciated the US military's efforts to try to limit the civilians killed in operations in Iraq and Syria, the use of the roof knock on the house in Mosul did not seem well planned.

"This is first time this has ever been used by the coalition, and the civilians would not have had any idea what that meant — on this occasion it would not have been helpful," he said.

He also pointed out that the Israelis tend to use a non-explosive missile or a missile carrying a small explosive to deliver the roof knock, as opposed to the US military's use of a Hellfire missile.

"It doesn't sound like any roof knock the Israelis would do — a small inert bomb vs. a 100-pound Hellfire missile," he said. "How is a woman supposed to know what that was? I get why they did it, but I also understand why she thought the attack was over and went back into the house."

Woods said that dropping leaflets, phone calls, and text messages are more effective at informing civilians about an impending strike. He also said that the civilian casualties are only likely to increase as the Iraqis, Kurds, and US-led coalition forces use artillery and airstrikes to begin the offensive to drive Islamic State out of Mosul, Iraq's second largest city, where 1.5 million people live.

"We are really in the most dangerous phase of the air war where as civilians are concerned — with the two population centers of Raqqa and Mosul being bombed so heavily — and we are on target for this to be one of the worst months for civilian casualties," Woods said.

Gerstner said the US military may use the roof knock tactic again in the future should the opportunity arise.

Follow Benjamin Gilbert on Twitter: @benrgilbert

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