( CNN) America’s second-highest ranking military officer, Gen. Paul Selva, advocated Tuesday for “keeping the ethical rules of conflict in place lest we unleash on humanity a placed of robots that we don’t know how to control.”

Selva was responding to a question from Sen. Gary Peters, a Michigan Democrat, about his views on a Department of Defense directive that requires a human operator to be kept in the decision-making process when it comes to the taking of human life by autonomous weapons systems.