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The purpose of this thesis is to examine and shed light on the potential long-term effects of depleted uranium weapons on the environment and civilians while placing it in the legal context of the law of armed conflict, specifically in relation to the principle of proportionality in attack and the accompanying incidental harm assessment. The thesis question is, “do the potential long-term effects on the environment and civilians when using depleted uranium weapons form part of the incidental harm assessment when calculating proportionality in the attack?”

The thesis starts by explaining what depleted uranium is and why it is used in weapons. It then briefly presents the extent to which the weapon has been used historically. It then details the alleged long-term effects of the weapon on both the environment and health together with the accompanying debate and controversy regarding those effects. Thereafter, it sets out a brief summary of LOAC and the targeting framework, followed by a more detailed overview of the principle of proportionality. The thesis then delves into the more complex issues at hand concerning long-term effects, temporal scope, the causal link, and if the environment forms part of incidental harm. 

Based on the majority view of scholars, treaty interpretation and state practice the author concludes that long-term effects form part of the incidental harm. Further, the author concludes that long-term or reverberating effects have no decisive temporal scope. The only limiting factor is that the effect should be reasonably foreseeable for the commander planning the attack. Reasonably foreseeability is the test and causal link in determining what ‘may be expected’. The author also concludes that environmental damage is part of the incidental harm side of proportionality. 

In regard to the main question, the author concludes that the potential long-term effects of DU weapons on civilians do not form part of the proportionality calculation because they are merely too speculative and not reasonably foreseeable with regard to the current scientific state. However, the long-term environmental effects may form part of the proportionality calculus on an operational level due to the existence of more evidence that DU weapons used on a major scale could potentially affect the environment even though the risk is small, making it reasonably foreseeable to a certain degree.