One of the most important responsibilities for a military commander is the protection of his or her own troops. Military personnel are informed that they have a right, and even an obligation, to use force to defend themselves and their units against attack or imminent attack. This right, often called "unit self-defense," is recognized by militaries around the world and serves as a key element of militaries' Rules of Engagement (ROE). (1)
A significant amount of legal scholarship has focused on the meaning of national self-defense under international law, particularly following the September 11 attacks and the 2003 U.S. invasion of Iraq. Legal scholars, practitioners, and international courts have parsed the meaning of "armed attack," (2) argued over the legitimacy of anticipatory self-defense, (3) and debated application of the Caroline doctrine (4) in states that are unwilling or unable to prevent armed attacks by non-state actors. (5)These articles generally focus on when and how states can use force against another state, or within the territory of another state, in self-defense. Yet there has been little attention to when soldiers can use force under international law to defend themselves against attacks or threatened attacks.
In particular, the source and scope of the right of unit self-defense has not been carefully examined in academic literature. Military ROEs assert the right of unit self-defense and numerous articles presuppose that such a right exists--it seems intuitive that this must be the case. Yet there is no clear source for this right as it is not codified in any international convention or treaty. Perhaps for this reason, several scholars have stated that the right of unit self-defense must be a subset of the right of national self-defense reflected in Article 51 of the United Nations Charter. (6) But, as this Article argues, the right of unit self-defense does not fit comfortably within the national self-defense framework.
This is the first thorough examination of the jurisprudential basis for unit self-defense in military Rules of Engagement under international law. (7) This Article argues that the right of unit self-defense is derived from customary international law and that it must be separate and distinct from the right of national self-defense. This is not a purely academic distinction, as states are required to report all actions taken in national self-defense to the U.N. Security Council. Moreover, maintaining a distinction between unit and national self-defense would mitigate concerns generated by the International Court of Justice's (ICJ) conservative interpretation of the right of national self-defense under Article 51 of the U.N. Charter.
Part I of this Article describes the concept of unit self-defense, drawing on various countries' Rules of Engagement. Part II critiques the arguments that unit self-defense is a subset of national self-defense, noting key differences regarding when and how these rights can be exercised. Part III explains that unit self-defense, although not derived from Article 51, is nevertheless recognized under customary international law, as evidenced by state practice and opinio juris. Part IV argues that understanding unit self-defense as an independent right can help make sense of several of the perceived inconsistencies in the ICJ's jurisprudence on self-defense, most notably in the Case Concerning Military and Paramilitary Activities in and Against Nicaragua. (8) Part V discusses the similarities between individual and unit self-defense, and raises some additional questions that warrant further attention in the academic literature.
I. AN OVERVIEW OF UNIT SELF-DEFENSE
The right of unit self-defense is "fundamental to all international military codes" and Rules of Engagement. (9) It "allows a commander, or an individual soldier, sailor or airman the automatic authority to defend his or her unit, or him Or herself, in certain well defined circumstances. …