Warfare, with a history as old as humanity itself, has been predominantly conducted through the application of physical force to disrupt, degrade, or destroy physical assets. That long history has led to well-developed doctrine and principles for shows of force, deterrence, proportionality, and rules for warfare that rely on predictable and repeatable characteristics of the physical weapons employed. The advent of cyber warfare in the modern era, however, has illustrated that the assumptions used for the employment of kinetic weapons do not necessarily apply to the employment of cyber capabilities. For example, unlike a physical missile or bomb, it is difficult to predict the precise effects, measure the resulting proportionality, or estimate the collateral effects attendant to the use of a computer virus. As we discuss, the differences between kinetic weapons and cyber weapons are discernible, manageable, and have far-reaching implications for strategic military doctrine, planning, and operational employment in both power projection and defense.