The policy also encouraged the development of the first early warning systems. Conventional war, even at its fastest, was fought over days and weeks. With long-range bombers, from the start of a nuclear attack to its conclusion was mere hours. Rockets could reduce a conflict to minutes. Planners reasoned that conventional command and control systems could not adequately react to a nuclear attack, so great lengths were taken to develop computer systems that could look for enemy attacks and direct rapid responses.