The fog of war may confound weapons that think for themselves

THE SKIESUNIDIR of Israel have lit up in recent weeks with the sinuous trails of interceptors colliding with thick volleys of rockets fired from Gaza. These spectacular aerial duels show autonomous weapons at work. For, though each launcher of Iron Dome, Israel’s missile-defence system, is manned by soldiers, only a computer can keep up with the most intense barrages. “Sometimes in large salvos, you can't have men in the loop for every rocket,” says one Israeli soldier. It is largely an algorithm that decides where and when to fire.Iron Dome is a defensive system that attacks physical objects (the incoming rockets) in an aerial battle-theatre devoid of immediate civilian bystanders, albeit that falling debris could injure or kill someone. But one day similar latitude might be given to offensive weapons which fire at human enemies on the ground, in more crowded places. A new report by the United Nations Institute for Disarmament Research (), a think-tank, explains why that will be far harder than knocking rockets out of the sky.