As a concept, deterrence has been part of the military vernacular since antiquity. In his History of the Peloponnesian War, Thucydides quotes Hermocrates as stating, “Nobody is driven into war by ignorance, and no one who thinks that he will gain anything from it is deterred by fear.”2 In the 2,400 years since then, the domains for the conduct of military affairs have expanded from the original land and maritime domains to air, space, and now cyberspace. As warfighting expanded its scope, strategic theory did as well. Today, U.S. doctrine declares that the fundamental purpose of the military is to deter or wage war in support of national policy.3 Therefore, military strategists and planners have a responsibility to assess how adversaries may be deterred in any warfighting domain. Through the joint planning process, planners, working through the interagency process, consider deterrent options for every instrument of national power—diplomatic, informational, military, and economic—across all phases of military operations.4 However, most of the thought and analysis in deterrence has revolved around the use of conventional and nuclear weapons.