In this paper we examine the ethical implications of emerging Nanotechnologically Enhanced Combat Systems (or 'NECS'). Through a combination of materials innovation and biotechnology, NECS are aimed at making combatants much less vulnerable to munitions that pose a lethal threat to soldiers protected by conventional armor. We argue that increasing technological disparities between forces armed with NECS and those without will exacerbate the ethical problems of asymmetric warfare. This will place pressure on the just war principles of jus in bello, (...) by encouraging the resort to tactics that either (i) make it more difficult to respect these principles or (ii) directly violate them, by virtue of attacking non-combatants or creating disproportionate numbers of casualties without a clear military goal. (shrink)