Georgetown University’s Bruce Hoffmann, author of Inside Terrorism, sketches a very grim scenario: “Picture Paris on November 13, 2015”—the night when people were slaughtered at a rock concert and in sidewalk cafés—“with drone attacks superimposed on top of it. Authorities would have been completely overwhelmed. This elevates our greatest fear, which is simultaneous urban attacks—now with swarming on top of them.”

On the battlefield, multiple coordinated drone attacks by ISIS already are happening. CBS News reported from the front in Mosul on Saturday that U.S.-backed Iraqi government operations to retake the western part of the city are being disrupted by “swarms of three to five” commercial quad copters modified to carry small grenades or artillery shells.

ISIS boasts about its new weapon, publishing photographs of its recruits in a classroom studying drones. The young men look like they’re there for vocational training, but the vocation is jihad. ISIS has also posted live-action videos taken by its little birds hovering over targets, then dropping explosives with surprising accuracy, including down the hatch of an armored car.

But in the context of urban terror such as Hoffman describes, the use of drones to harass and distract is especially problematic.