Navies perceive benefit from proclaiming the intent to acquire ‘fully environmentally compliant’ warships, but such statements indicate minimal understanding of what is entailed, or realisation of the emasculation of ships’ operational effectiveness inherent to such ambition. Inescapable technical realities further void any possibility of achieving this aspiration in all but limited circumstances. Navies need to be smarter in objectively characterising and managing environmental risks, and innovative in generating bespoke technical solutions. Compliance with International Maritime Organization (IMO) marine environment protection obligations can be exceptionally onerous for warships, and in many cases nonsensical to pursue and arguably impossible to achieve. It is also ever more divergent from the standard caveat of ‘not impairing the operations or operational capabilities of such ships’. Extant, emergent and forecast regulations address matters such as fuel consumption, speed limits, fuel tank protection, and ship materials. Some requirements can be accommodated, offering benefits in terms of operational effectiveness and sustainment. Many, however, cannot be addressed without penalty in combat capability, survivability and through-life costs. IMO rules are founded upon merchant ship risks and linked merchant ship solutions; strict application of merchant ship risk remedies to warships can result in inappropriate design responses to ill-defined, inconsequential or non-existent risks. The design and acquisition processes of warships are also incompatible with IMO implementation schedules. Myopic application to warships of IMO prescripts can result in perverse outcomes which actually amplify risks to the environment. Novel ways in which to demonstrate effective compliance with the intent of rules need to be adopted. Sensible environment protection should remain a policy goal, but implementation should only be on an innovative, judicious, and risk-assessed basis if warships are to accentuate operational capabilities, which, axiomatically is the base reason for their existence. It is incumbent upon navies to also manage wider regulatory and policy dimensions. This can only be achieved by generating a clear understanding of what compliance entails in terms of capability and technical risks and how this may relate to a navy’s core mission — to fight and win at sea. This must then be communicated as a cogent and reasoned argument to regulators and policy makers. This is so that commitments by navies to ‘environmentally compliant warships’ are neither arbitrary nor to the detriment of capability.