This chapter examines international obligations imposed on all States to protect and preserve the marine environment in relation to submarine operations. However, the sovereign immunity of military submarines significantly impacts both the applicability and enforcement of international marine environmental law. At present, nuclear powered and nuclear armed submarines pose the greatest environmental risks, and we discuss nuclear liability regimes, the possible relevance of nuclear-free zone treaties, and environmental obligations when decommissioning nuclear submarines. The obligation to prevent, reduce and control marine pollution may also be relevant in the context of sonar being used to detect submarines, as concerns have arisen as to the negative implication for marine mammals. While there have been various legal initiatives to address noise pollution, it is apparent that the consequences for military submarines is slight.