Rules of Engagement in Large Scale Combat Operations

As the focus of U.S. military doctrine and contingency planning shifts from counterinsurgency (COIN) campaigns toward large-scale combat operations (LSCO), Judge Advocates must anticipate changing operational law issues. In this environment, developments regarding the role of rules of engagement (ROE) in future U.S. military operations cannot be overlooked. Perhaps counterintuitively, ROE will likely play a significant role in future LSCO, as the principal mechanism for operationalizing and shaping U.S. “limited war” strategies in an armed conflict against an enemy great power.

The renewed emphasis on LSCO is derivative of a broader shift in U.S. strategic focus toward great power competition and conflict. In this geopolitical environment, large-scale conventional warfare between the United States and a rival great power, such as Russia or China, is a distinct possibility. Any such conflict, however, is unlikely to be the kind of “total war” experienced from 1939 to 1945. Instead, any future U.S. LSCO against Russia or China will almost invariably be carried out in the context of a “limited war.” Judge Advocates and operational planners should anticipate the need to craft and navigate an extensive network of ROE that will constrain and shape the conduct of hostilities.

Great Power War and Limited War

Since the end of the First World War, and particularly since the onset of the “nuclear revolution” in warfare, great power armed conflict has been increasingly defined by “limited war,” hostilities in which the belligerents deliberately calibrate the manner and extent to which they employ armed force against each other to manage escalation. U.S.-Soviet hostilities in the Cold War are the principal example of this phenomenon. For most of the Cold War, there was an inherent risk that U.S.-Soviet hostilities could escalate into an unbounded “general war” between the superpowers involving the mass employment of nuclear arms.

That potential, however, did not prevent the outbreak of major U.S.-Soviet hostilities. 1945 to 1991 witnessed a series of “proxy wars” in which the superpowers largely engaged in hostilities indirectly, by providing various types of military support to State and non-State surrogates that directly engaged in combat against the opposing superpower or its allies. Critically, many of those conflicts involved significant mutual and opposing U.S. and Soviet participation in hostilities centered on LSCO.

In those cases where significant direct U.S.-Soviet hostilities occurred, Soviet combat elements took part in those hostilities on a covert basis. Likewise, U.S. LSCO in Korea and Vietnam were subject to substantial geographic limitations. And U.S. and Soviet participation in LSCO conducted by their allies in a myriad of U.S.-Soviet proxy wars—such as the 1973 October War—most often took the form of a supporting role.

U.S.-Soviet hostilities were conducted on that basis because both the United States and the Soviet Union limited their use of armed force against each other in an attempt to ensure that deliberate escalation would achieve specific strategic effects against the enemy that would outweigh the associated risk of unintentional escalation to total war. Given the magnitude of potential damage associated with total war in the nuclear age, the effect of that mutual calculus was that major U.S.-Soviet hostilities during the Cold War were intentionally confined to a series of bounded geographies and conducted on a scale well below the superpowers’ full capacities to produce violence. Likewise, mutual and opposing U.S. and Soviet participation in large-scale conventional warfare was characterized by a series of calculated restrictions on the role of U.S. and Soviet forces in combat operations as well as the quantity and quality of military support provided to allies. In many cases, superpower involvement in hostilities was purposefully unacknowledged.

Limited War and Future Battlefields

Future great power wars (including potential U.S. conflicts with Russia and/or China) are likely to mirror the same fundamental strategic rationales that led to “limited war” between the United States and the Soviet Union. Like the Soviet Union, both Russia and China are nuclear-armed powers with significant conventional military capabilities. Moreover, recent hostile interactions between the United States and either Russia or China have shown concern over escalation that reflect U.S. and Soviet thinking on limited war in the Cold War.

In the Russo-Ukrainian War, for example, the United States has gradually increased the amount and sophistication of the military matériel it has supplied to Ukraine in accordance with changing assessments regarding the likelihood of major Russian retaliation. It has also conspicuously ruled out deploying combat forces to Ukraine for the express purpose of avoiding direct U.S.-Russian hostilities. However, U.S. military capabilities have been used to provide Ukrainian forces with critical operational, intelligence, and logistical support.

Likewise, Russia has repeatedly asserted that the United States and other Western countries are at war with it because they are providing extensive military support to Ukraine. However, Russia has not used conventional military force to target elements of the logistical infrastructure that supports U.S. and allied arms deliveries to Ukraine that are located in NATO territory. Instead, despite repeatedly threatening such escalation, it has limited its operations against those assets to sabotage activities. Critically, multiple strategists have assessed that Russia has exercised such restraint for fear of precipitating a major conventional war with NATO.

While none of the foregoing precludes U.S. involvement in conflict against Russia or China, it does demonstrate that future U.S. involvement in LSCO against an enemy great power will tend to be like that which has prevailed in the Russo-Ukrainian War. During those hostilities or in a separate contingency, the most likely circumstances in which U.S. military forces will be engaged in LSCO against Russia or China will involve those forces furnishing various forms of military support to allied and partner forces. Even if that includes a direct combat role for U.S. forces, it is most probable that such a role will be highly limited.

The implication is that in the most probable situations, U.S. operations will be subject to significant policy restraints. These include whether (and how) they can use offensive force against the enemy, the geographies in which they are permitted to operate, and which types of assistance they can provide to friendly forces.

ROE and Limited War

In U.S. military doctrine, ROE describe “directives issued by competent military authority that delineate the circumstances and limitations under which United States forces will initiate and/or continue combat engagement with other forces encountered.” Unlike law of armed conflict (LOAC) requirements, ROE are not legal rules, but policy directives articulated in military orders to ensure that U.S. forces conduct hostilities in accordance with national policy objectives, particularly when communication with higher authorities is limited or unavailable. That fundamental purpose—placing policy restrictions on the conduct of hostilities—makes ROE highly relevant to LSCO in limited war.

During the Cold War, when U.S. combat forces conducted LSCO against the Soviet Union or its proxies, modern-style ROE and their historical antecedents were integral to the effective execution of U.S. limited war strategies. Notably, historical precedents demonstrate that in situations of limited war against an enemy great power, ROE have been used to restrict lower-level commanders’ discretion to make decisions about the conduct of LSCO that implicate the State’s authority to use armed force on the international plane. In other words, in LSCO between great powers, ROE are used to operationalize national-level policy determinations regarding the extent to which the State will employ its available jus ad bellum authorities to engage in hostilities against the enemy.

In prior limited wars, this has primarily been accomplished by using ROE to place geographic and targeting restrictions on lower-echelon commanders’ authority to conduct offensive combat operations. Those ROE have prohibited lower-level commanders from prosecuting hostilities against certain enemy territories, military forces, or objects that could otherwise clearly be made the object of attack under LOAC in order to retain national-level control over the degree of armed force employed against enemy belligerents.

In Korea, for example, orders from the President and the Joint Chiefs of Staff (JCS) to the theater commander explicitly prohibited U.S. air attacks on Chinese territory from the outset of the war. Through this directive, the President withheld command authority to determine whether the operational advantage of attacking the enemy’s strategic rear support areas outweighed the escalation risk of extending active hostilities to Chinese territory. Another series of orders specifically prescribed the actions that U.S. forces were to take if “major Soviet units” were overtly employed in South Korea, thereby retaining national-level control over the U.S. military response to an expansion of the Soviet combat role.

Similarly, during the Vietnam War, in Operation Rolling Thunder, U.S. attacks against critical infrastructure vital to the North Vietnamese war effort—such as ports, railways, and petroleum facilities—required approval from the Commander in Chief of Pacific Command or even the President. The primary reason for those restrictions was that the President sought to carefully calibrate the intensity of U.S. hostilities against North Vietnam and its allies.

Moreover, in past limited wars, ROE have been used to operationalize changing national-level decisions on the use of force against enemy belligerents. The geographic and targeting limitations initially placed on lower-echelon commanders’ authority to conduct hostilities may be loosened or further restricted based on national-level determinations to increase or decrease the degree of armed force being employed against certain enemy belligerents. Those changes to ROE may be predicated upon changing strategic realities that lead to an expansion or contraction of the State’s jus ad bellum authorities in the relevant armed conflict.

During the Vietnam War, for example, a series of modern, mission-specific ROE were used to update further delegations of presidential command authority to lower-level commanders amid increased Soviet involvement in that conflict. For much of the war, attacks against specific target types or geographies that could threaten Soviet interests were subject to significant restrictions. However, in response to the 1972 Easter Offensive—a large-scale North Vietnamese invasion made possible by extensive Soviet logistical support—President Nixon removed many of those limitations for the explicit purpose of interdicting the supply of military matériel from the Soviet Union to North Vietnam. Critically, significant aspect of that authorization— presidential approval to intentionally threaten Soviet merchant shipping with destruction by mining North Vietnam’s major ports—was informed by the conclusion that using armed force to sever Soviet sea lines of communication with North Vietnam had become both strategically necessary and a proportionate measure of self-defense under the jus ad bellum.

In future U.S. LSCO against an enemy great power, therefore, the ROE are likely to be dominated by a series of geographic and targeting restrictions that limit authority to conduct hostilities against enemy belligerents. These constraints can be expected to change in accordance with strategic developments that impact legal authorities and drive national-level policy determinations regarding the extent to which those authorities will be fully employed.

Conclusion

The historical precedents articulated above suggest that the most probable character of any future great power conflict involving the United States will be that of a “limited war.” In such a conflict, U.S. forces are likely to operate under ROE that place a myriad of policy restraints on the conduct of hostilities beyond inherent LOAC restrictions. These policy constraints, moreover, are likely to constitute restrictions on the conduct of operations that derive from multiple sources, including strategic and policy considerations as well as jus ad bellum limitations on the use of force against enemy belligerents in an ongoing armed conflict. In view of such contingencies, U.S. defense planners should prepare for a future in which ROE continue to exert a significant influence on how, where, and when U.S. military forces conduct operations.

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Photo credit: Sgt Mark Webster RLC