The first public announcement of the U.S. using a “roof-knock” operation was made last Tuesday at a press briefing by Air Force Maj. Gen. Peter E. Gersten, deputy commander for operations and intelligence for the anti-ISIS Operation Inherent Resolve. In the briefing, Gersten described a strike against an ISIS cash distribution center on April 5, in Mosul, Iraq. “The bulk cash distribution site was used by ISIS to distribute money to fund terrorist activities,” Lieutenant Commander Ben Tisdale, a U.S. spokesman, said in a statement.

Prior to the attack—while air assets where on watch, circulating the clear sky above their AO—the U.S. recognized that their target contained several civilians, including the wife and children of one of the additional targets—an ISIS operative recognized as the emir of finance for ISIS. “He was the major distributor of funds to Daesh fighters. We watched him come and go from his house, we watched his supplies, we watched the security that was involved in it. And we also watched, occasionally, a female and her children in and out of the quarters.”

That’s where Maj. Gen. Gersten began looking for alternatives to avoid collateral damage and to give a heads-up to the civilians, encouraging them to leave prior to the strike. In addition to leaflets, another possible solution was brought to discussion.

One of Gersten’s experts (according to Gersten) suggested the Israeli tactic known as “roof knock,” which had been widely used in the recent Israeli conflicts in the Middle East. “We went so far as to actually put a Hellfire [missile] on top of the building and air-burst it so it wouldn’t destroy the building, but would instead simply knock on the roof to ensure that she and the children were out of the building,” he recounted. “Then, we proceeded with our operations.” Shortly afterward, two Mk84 general purpose (2,000 lb) bombs struck the facility, destroying “millions” of dollars in cash, but resulting in the death of six civilians nearby.