Nonlethal weapons are intended to provide their users with options in addition to lethal force. Proponents of such weapons suggest that they may be useful in a variety of military engagements or situations that are “less than war,” such as in peacekeeping and humanitarian involvements, in situations in which it is hard to separate combatants and noncombatants, or in civilian and military law enforcement contexts such as riot control or the management of violent criminals. In such situations, the use of lethal force is discouraged—and so new nonlethal weapons (such as tasers) have tended to substitute for older nonlethal weapons (such as billy clubs).
A key question concerning nonlethal weapons in combat is their relationship to traditional weapons—are nonlethal weapons intended to be used instead of traditional weapons or in addition to traditional weapons? For example, an acoustic weapon can be used to drive troops or irregular forces from an area or to dissuade a small boat from approaching a ship. But it can also be used to flush adversaries out from under cover, where they could be more easily targeted and killed with conventional weapons. The latter uses are explicitly permitted by NATO doctrine on nonlethal weapons:
Non-lethal weapons may be used in conjunction with lethal weapon systems to enhance the latter’s effectiveness and efficiency across the full spectrum of military operations.33
So it is clear that in at least some military contexts, military doctrine anticipates that nonlethal weapons can be used along with traditional weapons. But it is also clear that they are not always intended to be used in this way.
Another issue is whether the availability of nonlethal weapons in addition to traditional weapons creates an obligation to use them before one uses traditional weapons that are (by definition) more lethal. On this point, NATO doctrine is also explicit:
Neither the existence, the presence, nor the potential effect of non-lethal weapons shall constitute an obligation to use non-lethal weapons, or impose a higher standard for, or additional restrictions on, the use of lethal force. In all cases NATO forces shall retain the option for immediate use
33 Science and Technology Organization Collaboration and Support Office, Annex B: NATO Policy on Non-Lethal Weapons, available at http://ftp.rta.nato.int/public//PubFullText/RTO/TR/RTO-TR-SAS-040///TR-SAS-040-ANN-B.pdf.