A Comment On The Importance Of Reserves In Combat

An German Army A7V near the Somme on March 26, 1918 [forces.net] Operation Michael was the first of a series of German Army offensives on the Western Front in the spring of 1918. In late March, 74 German divisions employing infiltration tactics created a breach in a sector of the line held by the British Army. The Germans advanced up to 40 miles and captured over 75,000 British soldiers, but the ability of the British and French to redeploy reserves via rail halted the offensive in early April short of strategic success.

In response to my previous post on Trevor Dupuy’s verity regarding the importance of depth and reserves for successful defense, a commenter posed the following question: “Is the importance of reserves mainly in its own right, or to mitigate the advantages of attacker surprise?”

The importance of reserves to both attacker and defender is as a hedge against the circumstantial uncertainties of combat. Reserves allow attacking and defending commanders the chance to maintain or regain initiative in response to the outcomes of battle. The side that commits its last reserves before its opponent does concedes the initiative to the enemy, probably irrevocably.

In Trevor Dupuy’s theory of combat, the intrinsic superiority of the defensive posture (as per Clausewitz) is the corollary to the attacker’s inherent advantage in initiative. When combined with the combat multipliers of favorable terrain and prepared positions or fortifications, the combat power of a defending force is greatly enhanced. This permits a defending commander to reap the benefit of economy of force to create reserves. When arrayed in sufficient depth to prevent an attacker from engaging them, reserves grant flexibility of response to the defender. A linear defense or improperly placed reserves concede this benefit to the attacker at the outset, permitting the attacking commander to exploit initiative to mass superior combat power at a decisive point without reserves to interfere.

A defender’s reserves are certainly useful in mitigating attacker surprise, but in Dupuy’s theories and models, surprise is a combat multiplier available to both attacker and defender. As perhaps the most powerful combat multiplier available on the battlefield, surprise in the form of a well-timed counterattack by a defender can devastate an attacking force. Even an unexpected tactical wrinkle by a defender can yield effective surprise.

Interchangeability Of Fire And Multi-Domain Operations

Soviet “forces and resources” chart. [Richard Simpkin, Deep Battle: The Brainchild of Marshal Tukhachevskii (Brassey’s: London, 1987) p. 254]

With the emergence of the importance of cross-domain fires in the U.S. effort to craft a joint doctrine for multi-domain operations, there is an old military concept to which developers should give greater consideration: interchangeability of fire.

This is an idea that British theorist Richard Simpkin traced back to 19th century Russian military thinking, which referred to it then as the interchangeability of shell and bayonet. Put simply, it was the view that artillery fire and infantry shock had equivalent and complimentary effects against enemy troops and could be substituted for one another as circumstances dictated on the battlefield.

The concept evolved during the development of the Russian/Soviet operational concept of “deep battle” after World War I to encompass the interchangeability of fire and maneuver. In Soviet military thought, the battlefield effects of fires and the operational maneuver of ground forces were equivalent and complementary.

This principle continues to shape contemporary Russian military doctrine and practice, which is, in turn, influencing U.S. thinking about multi-domain operations. In fact, the idea is not new to Western military thinking at all. Maneuver warfare advocates adopted the concept in the 1980s, but it never found its way into official U.S. military doctrine.

An Idea Who’s Time Has Come. Again.

So why should the U.S. military doctrine developers take another look at interchangeability now? First, the increasing variety and ubiquity of long-range precision fire capabilities is forcing them to address the changing relationship between mass and fires on multi-domain battlefields. After spending a generation waging counterinsurgency and essentially outsourcing responsibility for operational fires to the U.S. Air Force and U.S. Navy, both the U.S. Army and U.S. Marine Corps are scrambling to come to grips with the way technology is changing the character of land operations. All of the services are at the very beginning of assessing the impact of drone swarms—which are themselves interchangeable blends of mass and fires—on combat.

Second, the rapid acceptance and adoption of the idea of cross-domain fires has carried along with it an implicit acceptance of the interchangeability of the effects of kinetic and non-kinetic (i.e. information, electronic, and cyber) fires. This alone is already forcing U.S. joint military thinking to integrate effects into planning and decision-making.

The key component of interchangability is effects. Inherent in it is acceptance of the idea that combat forces have effects on the battlefield that go beyond mere physical lethality, i.e. the impact of fire or shock on a target. U.S. Army doctrine recognizes three effects of fires: destruction, neutralization, and suppression. Russian and maneuver warfare theorists hold that these same effects can be achieved through the effects of operational maneuver. The notion of interchangeability offers a very useful way of thinking about how to effectively integrate the lethality of mass and fires on future battlefields.

But Wait, Isn’t Effects Is A Four-Letter Word?

There is a big impediment to incorporating interchangeability into U.S. military thinking, however, and that is the decidedly ambivalent attitude of the U.S. land warfare services toward thinking about non-tangible effects in warfare.

As I have pointed out before, the U.S. Army (at least) has no effective way of assessing the effects of fires on combat, cross-domain or otherwise, because it has no real doctrinal methodology for calculating combat power on the battlefield. Army doctrine conceives of combat power almost exclusively in terms of capabilities and functions, not effects. In Army thinking, a combat multiplier is increased lethality in the form of additional weapons systems or combat units, not the intangible effects of operational or moral (human) factors on combat. For example, suppression may be a long-standing element in doctrine, but the Army still does not really have a clear idea of what causes it or what battlefield effects it really has.

In the wake of the 1990-91 Gulf War and the ensuing “Revolution in Military Affairs,” the U.S. Air Force led the way forward in thinking about the effects of lethality on the battlefield and how it should be leveraged to achieve strategic ends. It was the motivating service behind the development of a doctrine of “effects based operations” or EBO in the early 2000s.

However, in 2008, U.S. Joint Forces Command commander, U.S Marine General (and current Secretary of Defense) James Mattis ordered his command to no longer “use, sponsor, or export” EBO or related concepts and terms, the underlying principles of which he deemed to be “fundamentally flawed.” This effectively eliminated EBO from joint planning and doctrine. While Joint Forces Command was disbanded in 2011 and EBO thinking remains part of Air Force doctrine, Mattis’s decree pretty clearly showed what the U.S. land warfare services think about battlefield effects.

Dupuy’s Verities: The Utility Of Defense

Battle of Franklin, 1864 by Kurz and Allison. Restoration by Adam Cuerden [Wikimedia Commons]

The third of Trevor Dupuy’s Timeless Verities of Combat is:

Defensive posture is necessary when successful offense is impossible.

From Understanding War (1987):

Even though offensive action is essential to ultimate combat success, a combat commander opposed by a more powerful enemy has no choice but to assume a defensive posture. Since defensive posture automatically increases the combat power of his force, the defending commander at least partially redresses the imbalance of forces. At a minimum he is able to slow down the advance of the attacking enemy, and he might even beat him. In this way, through negative combat results, the defender may ultimately hope to wear down the attacker to the extent that his initial relative weakness is transformed into relative superiority, thus offering the possibility of eventually assuming the offensive and achieving positive combat results. The Franklin and Nashville Campaign of our Civil War, and the El Alamein Campaign of World War II are examples.

Sometimes the commander of a numerically superior offensive force may reduce the strength of portions of his force in order to achieve decisive superiority for maximum impact on the enemy at some other critical point on the battlefield, with the result that those reduced-strength components are locally outnumbered. A contingent thus reduced in strength may therefore be required to assume a defensive posture, even though the overall operational posture of the marginally superior force is offensive, and the strengthened contingent of the same force is attacking with the advantage of superior combat power. A classic example was the role of Davout at Auerstadt when Napoléon was crushing the Prussians at Jena. Another is the role played by “Stonewall” Jackson’s corps at the Second Battle of Bull Run. [pp. 2-3]

This verity is both derivative of Dupuy’s belief that the defensive posture is a human reaction to the lethal environment of combat, and his concurrence with Clausewitz’s dictum that the defense is the stronger form of combat. Soldiers in combat will sometimes reach a collective conclusion that they can no longer advance in the face of lethal opposition, and will stop and seek cover and concealment to leverage the power of the defense. Exploiting the multiplying effect of the defensive is also a way for a force with weaker combat power to successfully engage a stronger one.

It also relates to the principle of war known as economy of force, as defined in the 1954 edition of the U.S. Army’s Field Manual FM 100-5, Field Service Regulations, Operations:

Minimum essential means must be employed at points other than that of decision. To devote means to unnecessary secondary efforts or to employ excessive means on required secondary efforts is to violate the principle of both mass and the objective. Limited attacks, the defensive, deception, or even retrograde action are used in noncritical areas to achieve mass in the critical area.

These concepts are well ingrained in modern U.S. Army doctrine. FM 3-0 Operations (2017) summarizes the defensive this way:

Defensive tasks are conducted to defeat an enemy attack, gain time, economize forces, and develop conditions favorable for offensive or stability tasks. Normally, the defense alone cannot achieve a decisive victory. However, it can set conditions for a counteroffensive or counterattack that enables Army forces to regain and exploit the initiative. Defensive tasks are a counter to enemy offensive actions. They defeat attacks, destroying as much of an attacking enemy as possible. They also preserve and maintain control over land, resources, and populations. The purpose of defensive tasks is to retain key terrain, guard populations, protect lines of communications, and protect critical capabilities against enemy attacks and counterattacks. Commanders can conduct defensive tasks to gain time and economize forces, so offensive tasks can be executed elsewhere. [Para 1-72]

UPDATE: Just as I posted this, out comes a contrarian view from U.S. Army CAPT Brandon Morgan via the Modern War Institute at West Point blog. He argues that the U.S. Army is not placing enough emphasis on preparing to conduct defensive operations:

In his seminal work On War, Carl von Clausewitz famously declared that, in comparison to the offense, “the defensive form of warfare is intrinsically stronger than the offensive.”

This is largely due to the defender’s ability to occupy key terrain before the attack, and is most true when there is sufficient time to prepare the defense. And yet within the doctrinal hierarchy of the four elements of decisive action (offense, defense, stability, and defense support of civil authorities), the US Army prioritizes offensive operations. Ultimately, this has led to training that focuses almost exclusively on offensive operations at the cost of deliberate planning for the defense. But in the context of a combined arms fight against a near-peer adversary, US Army forces will almost assuredly find themselves initially fighting in a defense. Our current neglect of deliberate planning for the defense puts these soldiers who will fight in that defense at grave risk.

Dupuy’s Verities: The Power Of Defense

Leonidas at Thermopylae, by Jacques-Louis David, 1814. [Wikimedia]

The second of Trevor Dupuy’s Timeless Verities of Combat is:

Defensive strength is greater than offensive strength.

From Understanding War (1987):

[Prussian military theorist, Carl von] Clausewitz expressed this: “Defense is the stronger form of combat.” It is possible to demonstrate by the qualitative comparison of many battles that Clausewitz is right and that posture has a multiplicative effect on the combat power of a military force that takes advantage of terrain and fortifications, whether hasty and rudimentary, or intricate and carefully prepared. There are many well-known examples of the need of an attacker for a preponderance of strength in order to carry the day against a well-placed and fortified defender. One has only to recall Thermopylae, the Alamo, Fredericksburg, Petersburg, and El Alamein to realize the advantage enjoyed by a defender with smaller forces, well placed, and well protected. [p. 2]

The advantages of fighting on the defensive and the benefits of cover and concealment in certain types of terrain have long been basic tenets in military thinking. Dupuy, however, considered defensive combat posture and defensive value of terrain not just to be additive, but combat power multipliers, or circumstantial variables of combat that when skillfully applied and exploited, the effects of which could increase the overall fighting capability of a military force.

The statement [that the defensive is the stronger form of combat] implies a comparison of relative strength. It is essentially scalar and thus ultimately quantitative. Clausewitz did not attempt to define the scale of his comparison. However, by following his conceptual approach it is possible to establish quantities for this comparison. Depending upon the extent to which the defender has had the time and capability to prepare for defensive combat, and depending also upon such considerations as the nature of the terrain which he is able to utilize for defense, my research tells me that the comparative strength of defense to offense can range from a factor with a minimum value of about 1.3 to maximum value of more than 3.0. [p. 26]

The values Dupuy established for posture and terrain based on historical combat experience were as follows:

For example, Dupuy calculated that mounting even a hasty defense in rolling, gentle terrain with some vegetation could increase a force’s combat power by more than 50%. This is a powerful effect, achievable without the addition of any extra combat capability.

It should be noted that these values are both descriptive, in terms of defining Dupuy’s theoretical conception of the circumstantial variables of combat, as well as factors specifically calculated for use in his combat models. Some of these factors have found their way into models and simulations produced by others and some U.S. military doctrinal publications, usually without attribution and shorn of explanatory context. (A good exploration of the relationship between the values Dupuy established for the circumstantial variables of combat and his combat models, and the pitfalls of applying them out of context can be found here.)

While the impact of terrain on combat is certainly an integral part of current U.S. Army thinking at all levels, and is constantly factored into combat planning and assessment, its doctrine does not explicitly acknowledge the classic Clausewitzian notion of a power disparity between the offense and defense. Nor are the effects of posture or terrain thought of as combat multipliers.

However, the Army does implicitly recognize the advantage of the defensive through its stubbornly persistent adherence to the so-called 3-1 rule of combat. Its version of this (which the U.S. Marine Corps also uses) is described in doctrinal publications as “historical minimum planning ratios,” which proscribe that a 3-1 advantage in numerical force ratio is necessary for an attacker to defeat a defender in a prepared or fortified position. Overcoming a defender in a hasty defense posture requires a 2.5-1 force ratio advantage. The force ratio advantages the Army considers necessary for decisive operations are even higher. While the 3-1 rule is a deeply problematic construct, the fact that is the only quantitative planning factor included in current doctrine reveals a healthy respect for the inherent power of the defensive.