Attacking Dams – Part I: Customary International Law

by | Jan 31, 2022

Attacking Dams - Part I

The New York Times recently reported on a March 2017 airstrike by U.S. forces against the Tabqa Dam, the largest in Syria. At the time of the attack, U.S. forces were supporting Syrian Democratic Forces (SDF) units trying to seize Tabqa, its airfield, and the dam from ISIS. According to the Times, special operations Task Force 9 called in the strike using a procedure designed for emergency self-defense situations, thereby circumventing the standard procedure for designating targets and approving strikes. Indeed, the dam was reportedly on a “no-strike” list.

The attack reportedly included the use of artillery and bombs, including a so-called “bunker-buster” with a BLU-109 Hard-Target Warhead. That system is designed to penetrate concrete, following which a delayed action fuze detonates 550 pounds of explosives inside the target. Fortunately, the weapon did not explode. Had it done so, experts believe the dam might have failed with disastrous consequences. Instead, witnesses say the attack caused equipment failure that resulted in a dangerous rise in the reservoir’s water level, sparked warnings to those downstream, and led Turkey to reduce the upstream flow into the reservoir.

The report follows on the heels of an earlier New York Times piece about a strike called in by Task Force 9 under the same procedure that caught the Combined Air Operations Center by surprise. Dozens of civilians were killed. These and other incidents, such as the mistaken drone strike during Kabul’s evacuation, motivated Secretary of Defense Austin to issue a directive last week on “Improving Civilian Harm Mitigation and Response.”

Commentary on the Tabqa Dam strike has focused on the attack’s risk to the civilian population and the use of special procedures for calling in the attack despite being on a no-strike list. However, attacks on dams raise complex international humanitarian law (IHL) issues. The rules governing them depend on the characterization of the conflict as international or non-international and whether the 1977 Additional Protocols I and II to the 1949 Geneva Conventions bind the attacking force.

Part I of this series examines the customary international law governing dam attacks. It is the law governing all U.S. operations against dams, including the attack on Tabqa Dam. In the second installment of the series, I will examine the rules for States Parties to the two 1977 Additional Protocols that provide so-called “special protection” for dams. That group includes most NATO Allies and other key partners of the United States, such as Australia and Japan.

The two posts are meant to help ensure that this and future dam strikes are measured against the proper legal standard. After all, dams will continue to be struck in future conflicts, for, as noted in the U.S. Army and Marine Corps’ Commander’s Handbook on the Law of Land Warfare, “A commander  may have a number of reasons to attack them, such as denial of electric power to military sources, use of forces contained therein to damage or destroy other military objectives (such as lines of communication), or to preempt enemy release of the dangerous forces to hamper the movement or advance of friendly forces” (paragraph 2-117).

Two points must be made before beginning. First, such attacks raise IHL issues beyond the lawfulness of attacks against them. Examples include whether the placement of military objectives in or near a dam violates either the requirement to take “passive precautions” to protect the civilian population from the effects of enemy attack or the prohibition on shielding. While those issues merit examination, they are beyond the scope of this series.

Second, the no-strike list issue, showcased by reporting, is a legal red herring. Striking a target on a no-strike or restricted-strike list (see here, here, and here) neither violates IHL nor constitutes a war crime. Such attacks may bear on issues like the attacker’s intent and whether appropriate “precautions in attack” were taken, but standing alone, hitting a no-strike or restricted-strike target is of no international law significance.

International Armed Conflict

Because the United States is not a Party to the 1977 Additional Protocols, customary international humanitarian law governs dam attacks mounted by its forces. The DoD Law of War Manual accurately restates the customary rule for international armed conflict,

Attack of facilities, works, or installations containing dangerous forces, such as dams, nuclear power plants, or facilities producing weapons of mass destruction, is permissible so long as it is conducted in accordance with other applicable rules, including the rules of discrimination and proportionality (section 5.13).

As we shall see in Part II, the “facilities, works, or installations containing dangerous forces” reference is drawn from the 1977 Additional Protocols. Interestingly, the Law of War Manual broadens the category to any target containing dangerous forces (like water or radiation), whereas the relevant Additional Protocols rules are, as will be explained, limited to dams, dikes, and nuclear electrical generating stations. Other entities containing dangerous forces, such as the weapon of mass destruction (WMD) production facilities cited in the Law of War Manual text, are governed for Parties to those instruments by the targeting rules they contain, which differ only slightly from customary IHL.

Reduced to essentials, the customary rule articulated in the Law of War Manual imposes no obligations on an attacker beyond the standard targeting rules. By them, a dam must qualify as a military objective, expected incidental injury to civilians or collateral damage to objects must be factored into the proportionality analysis to ensure it is not “excessive,” and an attacker must take precautions. The last requirement obligates the attacker to choose available weapons, tactics, targets, or aim points that will yield the desired effects with the least incidental injury or collateral damage.

In a classic 1978 article appearing in Naval War College Review, the late Hays Parks, then a Marine Corps Major, offered an example of how these rules apply.

During the Vietnam War, for example, the North Vietnamese installed substantial concentrations of antiaircraft guns and missiles on the earthenware dikes and dams surrounding Haiphong and Hanoi. Military necessity warranted airstrikes against these positions. However, attack of the positions with conventional ordnance would destroy not only the enemy positions but the dams as well. This would result in massive flooding and in the probable deaths of several hundred thousand civilians, a cost U.S. authorities concluded was disproportionate to the military advantage to be gained. When the mission finally was approved by President Nixon, it was executed with a clear proviso that only antipersonnel bombs, capable of neutralization of the positions without substantial damage to the dikes, would be used.

The Law of War Manual similarly notes that “cluster munitions have been used against military objectives containing dangerous forces, such as dams, in order to reduce the risk that bombardment of these objectives would release such forces and cause incidental harm to the civilian population” (section 6.13.).

Of course, installations containing dangerous forces merit special consideration during attacks because of the risk that the forces (water in the case of dams) might be released. The Law of War Manual highlights this operational reality.

In light of the increased potential magnitude of incidental harm, additional precautions, such as weaponeering or timing the attack such that weather conditions would minimize dispersion of dangerous materials, may be appropriate to reduce the risk that the release of these dangerous forces may pose to the civilian population.

The Army and Marine Corps’ Commander’s Handbook on the Law of Land Warfare makes precisely the same point (para. 2-118).

A slightly different tack is taken in the Navy, Marine Corps, and Coast Guard’s Commander’s Handbook on the Law of Naval Operations. It provides,

Dams, dikes, levees, and other installations, which if breached or destroyed would release floodwaters or other forces dangerous to the civilian population, should not be bombarded if the anticipated harm to civilians would be excessive in relation to the anticipated military advantage to be gained by bombardment (section

In other words, it emphasizes the centrality of the rule of proportionality when attacking dams. Other targeting rules, like the requirement to take precautions in attack, obviously continue to apply.

Non-international Armed Conflict

The strike on Tabqa Dam was governed by the customary law of non-international armed conflict because 1) that is the character of the U.S. hostilities with ISIS and 2) the United States is not a Party to the 1977 Additional Protocol II, a treaty examined in Part II of this series.

During non-international armed conflicts, the approach taken in the customary law of international armed conflict applies equally, a conclusion apparent in the Law of War Manual’s acceptance of the rules regarding military objectives, proportionality, and precautions during non-international armed conflicts (section 17.7). The San Remo Manual on the Law of Non-International Armed Conflict likewise supports this conclusion: “Attacking dams, dykes, or nuclear electrical generating stations is forbidden if the attack might cause the release of water or radioactivity and, as a result, excessive collateral damage to civilian objects and incidental injury to civilians” (section 4.2.3). Its commentary goes on to note, “particular care must be taken in attacking works and installations containing dangerous forces so as to avoid releasing those forces, thereby causing severe losses among the civilian population.”

Particular Care?

Notably, the International Committee of the Red Cross (ICRC) does not suggest that the dangerous forces rules in Additional Protocols I and II (see Part II of the series) reflect customary law. Rather, in Rule 42 of its Customary International Humanitarian Law study, the ICRC takes an approach to dam attacks during both international and non-international armed conflict that is similar to that outlined above.

Particular care must be taken if works and installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, and other installations located at or in their vicinity are attacked, in order to avoid the release of dangerous forces and consequent severe losses among the civilian population.

It might be contended that the ICRC’s restatement of customary law raises the threshold at which dam attacks may be launched through use of the mandatory language “must be taken,” as distinguished from the Law of War Manual’s “may be appropriate.”

However, the ICRC’s commentary to Rule 42 explains,

States’ sensitivity to the possibility of the release of dangerous forces is underscored by the fact that when attacks against such works and installations have been carried out in recent decades, the attacker stressed they were executed with the greatest care possible. It is further underlined by the condemnations of such attacks, denials of such attacks and generally by the restraint shown by States with respect to attacks against works and installations containing dangerous forces.

Placement of Tabqa Dam on the no-strike list is an excellent example of the fact that States take “particular care” when attacking targets that risk the release of dangerous forces.

The Army and Marine Corps’ Commander’s Handbook on the Law of Land Warfare’s emphasis on a commander’s responsibility during dam attacks supports the ICRC’s assertion of State sensitivity: “In light of the risks posed by attacks impacting these objectives, a commander should take additional care when contemplating an attack on a facility, work, or installation containing dangerous forces, or even an object located nearby” (paragraph 2-119). JCS Joint Publication 3-60, Joint Targeting, also acknowledges this reality as a matter of doctrine: “Attacks against installations containing dangerous forces—including dams, dikes, and nuclear power facilities—must be carefully considered for potentially catastrophic collateral damage” (Appendix A, para. 8a). Indeed, in the context of non-international armed conflict, the authors of the San Remo NIAC Manual, including myself, adopted the language of the Customary IHL study as a fair reflection of the law.

Finally, even if there were a difference as a matter of law between the care already required by IHL distinction rules such as precautions in attack and the “particular care” standard resident in the ICRC’s Rule 42, it would be difficult to imagine a situation in which an attacker took reasonable care in the circumstances, which includes the fact that dangerous forces are at risk of release, but unlawfully failed to take particular care.


 The customary law rules governing attacks on dams and military objectives in the vicinity of dams are those that govern other attacks on legally targetable persons and objects qualifying as military objectives. As a matter of law, it is not entirely clear that there is a requirement to take “particular care” when mounting such attacks. The better view is that there is, but whatever the case, in practice, IHL’s protection during dam attacks will derive primarily from the military objective, proportionality, and precautions in attack rules.

In Part II of the series, I will examine the special protection dams enjoy under the 1977 Additional Protocols I and II for States Party to those instruments.


Michael N. Schmitt is the G. Norman Lieber Distinguished Scholar at the United States Military Academy. He is also Professor of Public International Law at the University of Reading, Strauss Center Distinguished Scholar and Visiting Professor of Law at the University of Texas, and Professor Emeritus at the United States Naval War College.