The tactic consists of firing a warning missile above or near an intended target, to give residents time to flee before the real strike.
The Israeli military used such “roof knocks” in the 2014 operation in Gaza, in an effort to minimise civilian casualties.
The first public revelation of the U.S. using a “knock operation” came 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.
The U.S. used the tactic on 5th April in an operation in the Iraqi city of Mosul. One woman who initially did leave the targeted building but then ran back inside was killed, a US defence official said.
The U.S. had been closely watching the house of an ISIS finance operative, or “finance emir” in the words of Gersten: “He was the major distributor of funds to Daesh fighters”.
Using reconnaissance aircraft and other intelligence assets to keep watch, the U.S. then began to formulate a plan to get women, children and other civilians out of the building.
Gersten said: “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”.
Gersten acknowledged the Israeli influence, saying: “That’s exactly where we took the tactics and technique and procedure from”.