Numbers matter in war and warfare. Armies cannot function effectively without reliable counts of manpower, weapons, supplies, and losses. Wars, campaigns, and battles are waged or avoided based on assessments of relative numerical strength. Possessing superior numbers, either overall or at the decisive point, is a commonly held axiom (if not a guarantor) for success in warfare.
These numbers of war likewise inform the judgements of historians. They play a large role in shaping historical understanding of who won or lost, and why. Armies and leaders possessing a numerical advantage are expected to succeed, and thus come under exacting scrutiny when they do not. Commanders and combatants who win in spite of inferiorities in numbers are lauded as geniuses or elite fighters.
Given the importance of numbers in war and history, however, it is surprising to see how often historians treat quantitative data carelessly. All too often, for example, historical estimates of troop strength are presented uncritically and often rounded off, apparently for simplicity’s sake. Otherwise careful scholars are not immune from the casual or sloppy use of numbers.
However, just as careless treatment of qualitative historical evidence results in bad history, the same goes for mishandling quantitative data. To be sure, like any historical evidence, quantitative data can be imprecise or simply inaccurate. Thus, as with any historical evidence, it is incumbent upon historians to analyze the numbers they use with methodological rigor.
OK, with that bit of throat-clearing out of the way, let me now proceed to jump into one of the greatest quantitative morasses in military historiography: strengths and losses in the American Civil War. Participants, pundits, and scholars have been arguing endlessly over numbers since before the war ended. And since nothing seems to get folks riled up more than debating Civil War numbers than arguing about the merits (or lack thereof) of Union General George B. McClellan, I am eventually going to add him to the mix as well.
The reason I am grabbing these dual lightning rods is to illustrate the challenges of quantitative data and historical analysis by looking at one of Trevor Dupuy’s favorite historical case studies, the Battle of Antietam (or Sharpsburg, for the unreconstructed rebels lurking out there). Dupuy cited his analysis of the battle in several of his books, mainly as a way of walking readers through his Quantified Judgement Method of Analysis (QJMA), and to demonstrate his concept of combat multipliers.
I have questions about his Antietam analysis that I will address later. To begin, however, I want to look at the force strength numbers he used. On p. 156 of Numbers, Predictions and War, he provided the following figures for the opposing armies at Antietam:
The sources he cited for these figures were R. Ernest Dupuy and Trevor N. Dupuy, The Compact History of the Civil War (New York: Hawthorn, 1960) and Thomas L. Livermore, Numbers and Losses of the Civil War (reprint, Bloomington: University of Indiana, 1957).
It is with Livermore that I will begin tracing the historical and historiographical mystery of how many Confederates fought at the Battle of Antietam.