Based on the principle of distinction, the belligerent parties are obliged to respect the rule of precautions in attack. This rule supplements the general obligation to distinguish, at all times, between civilians and combatants, and between civilian objects and military objectives. In the fall of 2012 the Royal Norwegian Navy executed the first live firing of the Naval Strike Missile (NSM). One of the questions raised in this thesis is how the duty to take a precautionary “constant care” applies in NSM attacks. This is not easily stated since the Additional Protocol I to the Geneva Conventions (API) by its wording only apply on attacks on land, either from land to land, from sea to land or from air to land. Since the NSM is an operational fifth generation missile, the old discussion of wheter naval surface to surface missiles are able to distinguish between lawful targets and protected objects is once again considered with respect to new technology. The main part of the thesis, however is to address which rules the belligerent parties are obliged to follow as precautions in attack. This part of the thesis contains an analysis and discussion of API Article 57 and the San Remo Manual Article 46 and concludes with a 6-step process to simplify how to comply with international humanitarian law.