The worsening of the present security environment, which now includes the plausibility of a war breaking out, has renewed the search for deterrence and defence solutions. The complexity of hybrid threats makes it more challenging to prepare deterrence and defence capabilities against military aggression, which can result in the occupation of sovereign territory. In this paper, the idea explored is the deterrent value of resistance as an added layer of defence prepared in a whole-of-society defence strategy, increasing the cost to the adversary and contributing to national defence in retaking territory lost to occupiers. However, for resistance to be tactically and operationally effective to have a strategic effect, an element of command-and-control is needed to coordinate resistance activities in areas where government control has been lost. This case study of the US Special Forces and their role in the tactical and operational outcomes of the Civilian Irregular Defense Group (CIDG) program in Vietnam examines how contemporary Special Operations Forces, highly skilled in the conduct of unconventional warfare, can increase the cost to the enemy by operationalising civilian resistance and deny them from achieving their objectives, and this prospect can in turn deter the enemy from invading.