Chapter 2 will consider the concepts of unit and collective self-defence and draw a distinction with the concept of national self-defence. The use of force by warships in self-defence is first a question for commanders and should not necessarily amount to a conflict between states. It can extend only to the immediate defence of the warship, task group or vessels under escort, from targets which pose a direct threat. It does not extend to targets which do not pose a direct threat. Unit self-defence also does not extend to foreign warships or civilian vessels under escort unless there is agreement between the flag states concerned. In order to guide decisions by commanders, different indicia have developed for determining when an attack at sea is actually occurring and, therefore, when a warship may use force in self-defence. The highly contextual nature of establishing the intent of an opposing force, however, illustrates the limits of law in addressing these questions.