Logistics in Trevor Dupuy’s Combat Models

Trevor N. Dupuy, Numbers, Predictions and War: Using History to Evaluate Combat Factors and Predict the Outcome of Battles (Indianapolis; New York: The Bobbs-Merrill Co., 1979), p. 79

Mystics & Statistics reader Stiltzkin posed two interesting questions in response to my recent post on the new blog, Logistics in War:

Is there actually a reliable way of calculating logistical demand in correlation to “standing” ration strength/combat/daily strength army size?

Did Dupuy ever focus on logistics in any of his work?

The answer to his first question is, yes, there is. In fact, this has been a standard military staff function since before there were military staffs (Martin van Creveld’s book, Supplying War: Logistics from Wallenstein to Patton (2nd ed.) is an excellent general introduction). Staff officer’s guides and field manuals from various armies from the 19th century to the present are full of useful information on field supply allotments and consumption estimates intended to guide battlefield sustainment. The records of modern armies also contain reams of bureaucratic records documenting logistical functions as they actually occurred. Logistics and supply is a woefully under-studied aspect of warfare, but not because there are no sources upon which to draw.

As to his second question, the answer is also yes. Dupuy addressed logistics in his work in a couple of ways. He included two logistics multipliers in his combat models, one in the calculation for the battlefield effects of weapons, the Operational Lethality Index (OLI), and also as one element of the value for combat effectiveness, which is a multiplier in his combat power formula.

Dupuy considered the impact of logistics on combat to be intangible, however. From his historical study of combat, Dupuy understood that logistics impacted both weapons and combat effectiveness, but in the absence of empirical data, he relied on subject matter expertise to assign it a specific value in his model.

Logistics or supply capability is basic in its importance to combat effectiveness. Yet, as in the case of the leadership, training, and morale factors, it is almost impossible to arrive at an objective numerical assessment of the absolute effectiveness of a military supply system. Consequently, this factor also can be applied only when solid historical data provides a basis for objective evaluation of the relative effectiveness of the opposing supply capabilities.[1]

His approach to this stands in contrast to other philosophies of combat model design, which hold that if a factor cannot be empirically measured, it should not be included in a model. (It is up to the reader to decide if this is a valid approach to modeling real-world phenomena or not.)

Yet, as with many aspects of the historical study of combat, Dupuy and his colleagues at the Historical Evaluation Research Organization (HERO) had taken an initial cut at empirical research on the subject. In the late 1960s and early 1970s, Dupuy and HERO conducted a series of studies for the U.S. Air Force on the historical use of air power in support of ground warfare. One line of inquiry looked at the effects of air interdiction on supply, specifically at Operation STRANGLE, an effort by the U.S. and British air forces to completely block the lines of communication and supply of German ground forces defending Rome in 1944.

Dupuy and HERO dug deeply into Allied and German primary source documentation to extract extensive data on combat strengths and losses, logistical capabilities and capacities, supply requirements, and aircraft sorties and bombing totals. Dupuy proceeded from a historically-based assumption that combat units, using expedients, experience, and training, could operate unimpaired while only receiving up to 65% of their normal supply requirements. If the level of supply dipped below 65%, the deficiency would begin impinging on combat power at a rate proportional to the percentage of loss (i.e., a 60% supply rate would impose a 5% decline, represented as a combat effectiveness multiplier of .95, and so on).

Using this as a baseline, Dupuy and HERO calculated the amount of aerial combat power the Allies needed to apply to impact German combat effectiveness. They determined that Operation STRANGLE was able to reduce German supply capacity to about 41.8% of normal, which yielded a reduction in the combat power of German ground combat forces by an average of 6.8%.

He cautioned that these calculations were “directly relatable only to the German situation as it existed in Italy in late March and early April 1944.” As detailed as the analysis was, Dupuy stated that it “may be an oversimplification of a most complex combination of elements, including road and railway nets, supply levels, distribution of targets, and tonnage on targets. This requires much further exhaustive analysis in order to achieve confidence in this relatively simple relationship of interdiction effort to supply capability.”[2]

The historical work done by Dupuy and HERO on logistics and combat appears unique, but it seems highly relevant. There is no lack of detailed data from which to conduct further inquiries. The only impediment appears to be lack of interest.


 [1] Trevor N. Dupuy, Numbers, Predictions and War: Using History to Evaluate Combat Factors and Predict the Outcome of Battles (Indianapolis; New York: The Bobbs-Merrill Co., 1979), p. 38.

[2] Ibid., pp. 78-94.

[NOTE: This post was edited to clarify the effect of supply reduction through aerial interdiction in the Operation STRANGLE study.]

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Shawn Woodford
Shawn Woodford

Shawn Robert Woodford, Ph.D., is a military historian with nearly two decades of research, writing, and analytical experience on operations, strategy, and national security policy. His work has focused on special operations, unconventional and paramilitary warfare, counterinsurgency, counterterrorism, naval history, quantitative historical analysis, nineteenth and twentieth century military history, and the history of nuclear weapon development. He has a strong research interest in the relationship between politics and strategy in warfare and the epistemology of wargaming and combat modeling.

All views expressed here are his and do not reflect those of any other private or public organization or entity.

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  1. Thank you for the response. I am vaguely familiar with other epochs (models for roman army camp sizes are rather simplistic), the only obstacle I faced was to determine the “logistical limit” of modern day armies. I argue that the build up process of forces in a prolonged war of attrition is hampered by an insufficient supply system, directly linked to the organization of a military force, independent from the quantity of troops a nation can potentially field (aside from factors like economic strength and infrastructure), no matter the type. The US Army increased in size from 175,000 in mid 1939 to 1,400,000 in mid 1941 (the RKKA doubled in size during the 30s and it could not adequately supply the forces and field enough officers to render it effective). Yet in the ETO and MTO most of the concepts were based on improvisation rather than on the pre established plans.
    Attrition armies with large divisional slices have a limited benefit from high motorization, while the provident nature of operativ warfare troops can be beneficial in the mobilization effort, while also being exposed to combat for a shorter amount of time. They can operate and fight significantly longer under unbeneficial conditions but the chain of supply should remain equivalent (as well as air supply), experiencing similar difficulties. Mobile and more efficient armies should be able to feast on their enemies supplies. It is hard to believe that Temujin or Alexander possessed an advantage in logistics over their enemies.
    On the other side, a defender with backup/foreign aid can dramatically increase a nations abililty to feed troops into battle and extort a stalemate that may involuntarily transition into a grinding war of attrition.

    • Starting from the end of your post, have you had a read of Engel’s book – Alexander the Great and the Logistics of the Macedonian Army? He talks about how Phillip had reformed the echelon of the Army to eliminate a variety of ‘unnecessary’ elements (for one, non-combatants) to improve mobility. Furthermore, he examines how logistic analysis ultimately informed Alexander’s strategy- thus the advantage gained was through the thought process of a military commander and not necessarily logistic capabilities.

  2. An interesting post. Although a hunch, I tend to think the 65% of supply might be a little low. Alternatively, it might include non-critical supplies (canteen stores, clothing at times etc.). It’s a modelling tool I might investigate a little further. A major theme in Western armies is to reduce demand on logistic systems; for example, the US WW2 Army used 1 gallon of fuel per soldier, the ratio is now 1:25. Understanding the limits you can ‘push’ a force in terms of sustainment before combat power is influenced is critical.

    • 65% was a swag figure, but Trevor Dupuy had an uncanny knack for getting them close to correct. This would also have applied to 1940s era armies. I wonder just how much redundancy there might be in current just-in-time inspired lean sustainment? I suspect battlefield interdiction may become a critical element of Multi-Domain Battle given the increasing effectiveness of long-range precision fires capable of targeting logistical support vehicles throughout the battlespace. How many support vehicles can a force lose before it impinges on combat power?

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