Military ethics serve as a normative code of behaviour for the armed forces of a state, acting as a mechanism of definition and control within the force, between the force and its client, and between the force, its adversaries and the wider public. They have two, intrinsically linked, functions: a preventative function, which defines the moral and legal parameters of conduct, and a constructive function, which creates and maintains an effective and controllable force. Preceded by the code of chivalry, they were largely a creation of the era of conventional interstate warfare that was waged across the European continent from the Treaty of Westphalia through to the desolate end of the Second World War; yet, the operations upon which armed forces, and in particular, the New Zealand Army are deployed have changed, dramatically. Wars no longer, current operations are generally justified on moral principles and involve a multinational, joint and interagency deployment sent to intervene in an irregular, intrastate conflict occurring in an underdeveloped region and conducted under the intense glare of the media. This disjuncture between the changing nature of operations and the context in which military ethics were formulated provides the fundamental question for the thesis: if the milieu in which military ethics developed has changed significantly, what is their current utility? Using the New Zealand Army as the frame of reference, first the contemporary operational environment and then the specific operational environment in Timor-Leste were examined to assess the current utility of military ethics. It was found that the preventative function has an increasing utility because it ensures conduct is within expected norms in an era where the perception of the adversary, the local populace and the domestic and international audience is key to operational success. Despite the reduction in conflict intensity, the constructive function has a remaining utility through its mediation and amelioration of the stressors engendered by the growing complexity of the operational environment. The retention of utility for the constructive function appears to have been facilitated by an adaptation of the warrior ethos, from a narrow traditional outlook to a broad and comprehensive modern interpretation.