Do the Strikes on al Shabaab Stretch the AUMF or The Unit Self-defense Doctrine?

Charlie Savage’s piece on the legal basis for the March 5 U.S. strike against an al Shabaab training camp, which allegedly killed 150 fighters, raises the intriguing question of whether the AUMF has been stretched yet again, this time to justify U.S. operations against al Shabaab as a whole. The strike likely does represent an expansive interpretation of Article II authority and an erosion of limits on the use of force in undeclared armed conflict zones, but the bogeyman is not an expanded AUMF interpretation.

Savage notes that previously the Obama administration had distinguished between al Shabaab fighters considered part of al Qaeda and those operatives who wished to simply control territory in Somalia, with the AUMF providing authority to target the former but not the latter. Abandoning this distinction and stretching the AUMF to extend whenever there was a ‘continuing and imminent threat’ facing U.S. forces on an AUMF mission, the article would seem to argue, would erode existing limits on the AUMF. In Savage’s article, Bobby Chesney explains that such an interpretation could enable the government to “boot strap” unrelated missions to the AUMF wherever there was a ‘continuing and imminent threat’ to U.S. forces.

Chesney and the other authorities in Savage’s article are right that this position would seem to allow a much more flexible threats-based targeting model, unconstrained by the status-based limits imposed in the AUMF. However, the significant change here is not how broadly the AUMF legal authority is conceptualized but the way that soldiers’ inherent right to self-defense is used. When Savage asked whether the AUMF was the legal authority for the March 5 strike DoD’s spokesman Joe Sowers said that while the AUMF was deemed to bestow “authority for direct action against a limited number of targets in Somalia” who are deemed to be part of al Qaeda (quoting the April 2015 remarks of then-General Counsel Stephen Preston), this did not include the 150 presumed fighters killed on March 5, nor those killed in previous strikes in June, July, and November 2015. Instead, they were killed as part of a “tactical defense” of U.S. and AMISOM forces in Somalia based on evidence that the individuals posed a threat. This suggests that what justified the strike was a separate legal authority, often discussed only as a tactical rules of engagement issue, but available to troops wherever they are deployed independent of their force authorization – the right to unit self-defense.

U.S. troops have an inherent right to defend themselves or their unit against imminent threats wherever they are located, in peacetime and in wartime. As the U.S. standing rules of engagement describes it:

Unit commanders always retain the inherent right and obligation to exercise unit self-defense in response to a hostile act or demonstrated hostile intent.

This so-called individual or unit self-defense can also extend to other affiliated forces as well—which in this case would be the AMISOM forces—where designated in the mission rules of engagement.

The doctrine of unit or individual self-defense is long-standing, and is not limited to U.S. troops. All NATO allies have similar provisions. The right to respond in self-defense, and defense of others is also standard for all peacekeeping contingents now. There are debates about the origin of this right, with the U.S. arguing it flows from the sovereign right of self-defense, and other countries grounding it in domestic criminal law or in customary law, but soldiers’ right to self-defense is universally recognized.

While the existence of an inherent self-defense right is not new, the recent strike against al Shabaab demonstrates how it has expanded under the pressures of modern warfare. I have been working on an article that examines the scope of self-defense and how the U.S. and other NATO allies have applied this doctrine in Afghanistan and other recent engagements (In lieu of my forthcoming article, see this interesting Harvard Law School study on related topics). The reliance on self-defense as a rationalization to use force has grown in the last decade, in part due to the nature of conflict in places like Iraq and Afghanistan, where soldiers often did a lot more defending against IEDs and ambushes than using offensive force. In addition, restrictions on other types of offensive force (i.e. tactical directives like this one or this one), and possibly the difficulty of applying International Humanitarian Law theories to who was “participating in conflict” in the heat of combat, made reliance on self-defense a much easier, less scrutinized catch-all. At least for U.S. troops, it has become somewhat of a default.

The right of self-defense is not limited to ground troops. Disclosed cockpit recordings and after-the-fact investigations from aerial attacks and drone strikes also suggest that authorization to use force in those instances relies on a determination of self-defense, often triggered by seeing a threat in the form of a “hostile act” or a demonstration of “hostile intent.” A hostile act or hostile intent could be something as obvious as brandishing a gun—or what looks like a gun—or appearing to dig an IED, or it could be tactical maneuvering in ways that suggest a forthcoming attack, as with the Shabaab training camp. While not necessary, where supported by additional intelligence, the determination of hostile intent is that much stronger.

Self-defense should only be triggered by an imminent threat, but as the U.S. Standing Rules of Engagement make clear, “[i]mminent does not necessarily mean immediate or instantaneous,” (most US allies would disagree, maintaining a tighter imminence standard for individual self-defense). Yet while it is ambiguously constrained, this right is not unlimited. U.S. soldiers and military officials I interviewed said that the last foreseeable moment available to repel or stop the attack, when there would be no other time or opportunity to do so, was usually used to gauge the imminence standard. Authority to respond in self-defense then lasts as long as the individual “continues to commit hostile acts or exhibit hostile intent,” according to the Standing Rules of Engagement. These imminence thresholds are similar to those described by the Pentagon in justifying the May 5 strikes. When Savage asked Robert S. Taylor, the acting Pentagon general counsel, if this meant that the United States could strike all al Shabaab fighters at any time on the pretext that they posed a “continuing” threat, Taylor said no. The attack was only justified because the intelligence suggested an imminent threat and that this presented the “last, best opportunity” to stop it.

The clarification that the strike was not authorized under the AUMF, the description of this strike as a “tactical defense”, and the similarity of Taylor’s description of the imminence requirement to standing US interpretations of imminence suggest the strike was authorized under a theory of unit self-defense, in defense of the unit of Special Operations soldiers deployed in Somalia, and/or the AMISOM forces accompanying them. In short, the government did not have to stretch the AUMF to attack these 150 Shabaab fighters. The AUMF authorized the presence of the soldiers to fight al Qaeda-linked members of al Shabaab, and once in Somalia, their right of unit self-defense provided authority to repel an imminent threat to themselves and to designated forces working with them.

Assuming this was a self-defense response, what would the legal basis be under international and national law? Under international law, responses under individual self-defense exist in a strange limbo. International humanitarian law is silent on the right to self-defense, but it is a widely accepted principle that individual soldiers, or units of soldiers, have the right to defend themselves. Because it is an inherent right, the authorization to use force in individual or unit self-defense is considered to exist above and beyond the right to use force as a combatant in armed conflict. So, for example, even when Germany did not consider itself engaged in an armed conflict in Afghanistan and its soldiers were not authorized to take part in an armed conflict (up until mid-2009 privately, early 2010 publicly), its forces in Afghanistan could use force in self-defense.

The strike on the Shabaab training camp, if not based on authority granted by the AUMF but instead on self-defense, leaves open the question of what U.S. domestic authority would have supported the strike. The question does not usually arise because in most cases unit self-defense responses take place in the context of a declared armed conflict, which presumably is supported by other underlying domestic legal authorization. So in Afghanistan, for example, the domestic legal authority for such a response was not problematic. But as troops are increasingly deployed to engage in armed conflicts beyond “hot” battlefields, where the domestic authorization covers targeting only certain groups but not responding to the full panoply of potential threats, the source for this self-defense authority becomes increasingly important.

The most plausible source for an inherent self-defense right for soldiers that exists in both wartime and peacetime would be the president’s Article II authority as Commander-in-Chief. This has been used to justify not only limited operations in wartime, but also deployment of soldiers and their actions short of armed conflict. In a 1994 opinion, Deployment of the United States Armed Forces into Haiti, the Office of the Legal Counsel justified President Clinton’s deployment of 20,000 U.S. troops to Haiti under the president’s Article II authority. This is not the most helpful precedent given that the OLC justified the president’s decision not to go to Congress on the grounds that the “nature, scope, and duration” of the anticipated deployment did not make it a “war”, and that the situation did not seem likely to lead to “major or prolonged hostilities or serious casualties”. Neither could be said about the current situation in Somalia. However, Article II authority was also used in the 1992 OLC memo Authority to Use United States Military Forces in Somalia, which justified the deployment of U.S. troops to Somalia for the purpose of “good will or rescue, or for the purpose of protection American lives or property or American interests” (quoting a 1941 opinion by then Attorney General Robert Jackson, discussed here). The exercise of self-defense for troops who are on an authorized and legitimate mission, and are under imminent threat would certainly serve the purpose of protecting American lives and interests.

While Article II can be made to cover the exercise of unit self-defense in these nebulous armed conflict situations, as this analysis suggests, it can create an odd fit. And it should ring alarm bells—more than a potential expansion of the AUMF, which theoretically could be repealed or legislatively constrained. The right to self-defense, and thus theoretically the ability to use it expansively is not unique to Somalia or to AUMF-authorized situations. For example, as the U.S. has deployed trainers to assist forces opposing ISIL in Iraq and Syria, the Administration has made clear each step of the way that they were not there on a combat mission but would have the same right of self-defense as all troops. A repeat of the March 5 Somalia strike in Iraq or Syria on grounds of unit self-defense would be highly plausible.

If unit self-defense is now being used in this way, it reinforces the argument Bobby Chesney made that regardless of the scope (or existence) of the AUMF, since 9/11, the U.S. has adopted a legal model for countering perceived threats that effectively makes such legislative authorizations superfluous. Chesney argues that this “continuous threat model,” as he frames it, essentially boils down to “a claim about the president’s authority to direct the use of military force as an exercise of national self-defense even in the absence of explicit Congressional authorization.” Unit and individual self-defense does not support this on its own – soldiers still have to have an underlying authorization for their deployment. However, if used in this expansive way where soldiers have been deployed, unit and individual self-defense can aid and abet this model by making authorization to respond to threats available wherever U.S. soldiers are present. Until this point, unit self-defense has not been used in this way. It has overwhelmingly been used to justify uses of force within a declared armed conflict zone. But that may be changing. Perhaps this is another point to Chesney’s argument that any existing restraints have been more a reflection of policy than of limits on the underlying legal model.

IHL lawyers often disdain discussions of self-defense or hostile intent as a “rules of engagement” issue. But in reality this doctrine is justifying an increasingly wide use of force in declared, and not so declared, armed conflict zones. Ignoring it may lead to mis-ascribing certain actions or strikes to other doctrines, such as taking the March 5 strike as evidence of an ever-inflating AUMF authorization. It also might lead scholars or commentators to miss possibly even more concerning trends in warfare, including how expansive use of this doctrine may erode limitations on use of force under both international and domestic law.