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.

Dupuy’s Verities: The Requirements For Successful Defense

A Sherman tank of the U.S. Army 9th Armored Division heads into action against the advancing Germans during the Battle of the Bulge. {Warfare History Network]

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

Successful defense requires depth and reserves.

From Understanding War (1987):

Successful defense requires depth and reserves. It has been asserted that outnumbered military forces cannot afford to withhold valuable firepower from ongoing defensive operations and keep it idle in reserve posture. History demonstrates that this is specious logic, and that linear defense is disastrously vulnerable. Napoleon’s crossing of the Po in his first campaign in 1796 is perhaps the classic demonstration of the fallacy of linear (or cordon) defense.

The defender may have all of his firepower committed to the anticipated operational area, but the attacker’s advantage in having the initiative can always render much of that defensive firepower useless. Anyone who suggests that modern technology will facilitate the shifting of engaged firepower in battle overlooks three considerations: (a) the attacker can inhibit or prevent such movement by both direct and indirect means, (b) a defender engaged in a fruitless firefight against limited attacks by numerically inferior attackers is neither physically nor psychologically attuned to making lateral movements even if the enemy does not prevent or inhibit it, and (c) withdrawal of forces from the line (even if possible) provides an alert attacker with an opportunity for shifting the thrust of his offensive to the newly created gap in the defenses.

Napoleon recognized that hard-fought combat is usually won by the side committing the last reserves. Marengo, Borodino, and Ligny are typical examples of Napoleonic victories that demonstrated the importance of having resources available to tip the scales. His two greatest defeats, Leipzig and Waterloo, were suffered because his enemies still had reserves after his were all committed. The importance of committing the last reserves was demonstrated with particular poignancy at Antietam in the American Civil War. In World War II there is no better example than that of Kursk. [pp. 5-6]

Dupuy’s observations about the need for depth and reserves for a successful defense take on even greater current salience in light of the probably character of the near-future battlefield. Terrain lost by an unsuccessful defense may be extremely difficult to regain under prevailing circumstances.

The interaction of increasing weapon lethality and the operational and human circumstantial variables of combat continue to drive the long-term trend in dispersion of combat forces in frontage and depth.

Long-range precision firepower, ubiquitous battlefield reconnaissance and surveillance, and the effectiveness of cyber and information operations will make massing of forces and operational maneuver risky affairs.

As during the Cold War, the stability of alliances may depend on a willingness to defend forward in the teeth of effective anti-access/area denial (A2/AD) regimes that will make the strategic and operational deployment of reserves risky as well. The successful suppression of A2/AD networks might court a nuclear response, however.

Finding an effective solution for enabling a successful defense-in-depth in the future will be a task of great difficulty.

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.