Imagine a major war during which the US Army conducts large-scale combat operations in a place where COVID-19 has hit. A few soldiers show symptoms within just a few days of units entering the disease-stricken area of operations, with progressively more added over the next few weeks. The Army faces a choice as to whether the enemy or the disease is the main threat. At the same time the Army could quickly find itself with responsibility for civilians in the consolidation area, a responsibility that in the case of major outbreak is personnel- and resource-intensive. As soldiers sicken operations become more costly or cease altogether. This disturbing picture raises the question: How might the Army fight or even operate in such an environment and how should it prepare?

The obvious answer would be to avoid such situations but this may very well prove impossible. As the history of large-scale combat operations (LSCO) among great powers suggests, planning for these operations means planning for outbreaks, and planning to win means that disease has to be a primary concern of all commanders, not just the Army Health System.

During the Second World War the United States faced situations similar to the scenario envisaged above. The typhus outbreak during the war was widespread and devastating. During the years of the US military’s North Africa Campaign, there were more than 102,214 cases of typhus in the countries in which the campaign took place. In Egypt between 1942 and 1943 there were more than seventy-two thousand cases. The losses among the force and the civilian population presented a significant operational challenge to the US Army. The threat of typhus was so great that President Franklin D. Roosevelt created the United States of America Typhus Commission in December 1942 to control the outbreak.

Typhus was not the only disease that caused major operational challenges during the Second World War. In the US military there were ninety thousand cases of Dengue and 470,000 cases of malaria. During Guadalcanal campaign, tropical diseases had disabled around two-thirds of the 1st Marine Division. This contributed to the decision to withdraw the division, which in turn led to a halt of the campaign. The scale of the outbreak also left the division combat-ineffective for months after the campaign. While fighting around Sansapor on Dutch New Guinea, unanticipated disease proved as much, if not more, of a threat than Japanese actions. Within five days of the first soldier coming to the attention of medical personnel with the symptoms of scrub typhus, 135 soldiers had fallen ill. In certain areas the disease was so devastating that outposts had to be abandoned. The disease rendered the 1st Infantry Regiment entirely combat-ineffective. For these units the disease casualties far exceeded the threshold of a medical, or even tactical, problem. The rates and sheer number of losses posed a problem for operational and strategic commanders.

Hepatitis similarly caused massive disruption to the Allied operational force in the Second World War. Some British Army regiments in the Mediterranean Theater of Operations lost as much as 9 percent of their effectiveness due to hepatitis. The problem for the US Army was equally severe; between 1942 and 1945 hepatitis infected 182,383 personnel. In the Middle East Theater, this meant a hospitalization rate within the US Army of around 16.7 percent. The loss of manpower was such that the Army Epidemiological Board created a special committee to deal with hepatitis specifically. What is particularly interesting about the case of hepatitis is that while it was a well-known disease before the war, its impact on the war was not taken into sufficient account during planning. This may be explained by the fact that the US Medical Department based its models for disease and casualties on the experience of the previous large-scale war—in this case the First World War, in which hepatitis was not a major problem for US personnel. As a result, the models and preparations for the outbreak proved insufficient.

This is not only a historical problem—it could easily become a contemporary one, as well. Anecdotal evidence suggests that diseases like Q fever and tuberculosis caused problems in Iraq and Afghanistan. However, given the nature of those conflicts, sick soldiers could be isolated, treated, and replaced without a significant impact on the war effort. This is less likely to be true for an operational force engaged in LSCO. Under such conditions, similar rates of manpower loss to disease as those seen during the Second World War could have consequences that would be nothing short of catastrophic.

There are several reasons outbreaks such as those encountered in the Second World War would pose a particular problem during LSCO among great powers. Great-power conflict often takes on a global nature. For the United States, this means that its forces operate in areas of the world with which they are unfamiliar or in which they rarely have a large presence. This exposes the force to diseases with which the Army is less familiar. Additionally, if these areas are less populated, a given disease may be uncommon in human populations but placing forces in the area would greatly increase human exposure. This was the case with scrub typhus, for example.

Moreover, LSCO itself is often responsible for the creation of large outbreaks. There are two primary mechanisms by which engaging in LSCO causes unanticipated outbreaks. In the first case, the Army itself becomes the vector that spreads a disease and causes an outbreak. Unlike in comparatively more limited stability or counterinsurgency operations, the fast pace of LSCO means that soldiers are less isolated from the conditions of the general populations in the areas in which operations take place. This means they are more likely to be exposed to local diseases and critically, as soldiers move—either operationally or through sustainment pipelines—they become a perfect mechanism to spread disease. This was one of the primary factors that led to the severity of the typhus outbreak during the Second World War. As units and soldiers moved and refugees were repatriated, they spread the outbreak into areas that were usually free of the disease. The speed of modern militaries and the tempo anticipated for future great-power conflicts greatly increases this challenge and the threat it poses.

In addition to spreading outbreaks, the high-tempo nature of LSCO can cause them. The typhus epidemic in Naples during the winter of 1943–44 provides an example of the mechanism by which this happens. Prior to this period, there had been sporadic cases of typhus in Naples, but the conditions of a city involved in LSCO changed that. Allied bombardment devastated the city’s infrastructure, including its sanitation infrastructure. This allowed for proliferation of disease. As the population attempted to avoid the bombardment and fighting, civilians sought protection in overcrowded shelters, which enabled rapid transmission. The destruction of infrastructure and a lack of food weakened the population and the resilience of the city, which in turn increased the severity of the outbreak. Finally, the degradation of medical response and capacity within the city meant that the outbreak was able to rapidly overwhelm available resources. By November 1943, admission of new typhus cases in Naples hospitals surpassed twenty-five per day. Through the next two months, the situation deteriorated to the point that the first week of January alone saw approximately seven hundred people die from Typhus in Naples. By this point, the disease threatened to wipe out the city.

The case of Naples demonstrates the means by which the prosecution of LSCO can cause a severe outbreak in an area that was previously largely unaffected. It also indicates the particular challenges posed by urban terrain. The destruction of sanitation infrastructure, the effect of crowding and sheltering, as well the removal of resources on which the population of a city relies all greatly increases the chance for and severity of an epidemic. Given the increased lethality and destructive power projected for future LSCO scenarios, these effects will only increase in magnitude. With the growing scale and scope of urban terrain it will likely prove impossible to avoid engagement in those areas most vulnerable to the creation of an epidemic.

While the examples from the Second World War are of diseases for which there are now protocols, there were none at the time. The emergence in recent decades of a host of threats such as MERS, SARS, H1N1, and now COVID-19 demonstrate that the potential to encounter previously unanticipated diseases remains significant. As it thinks about a return to great-power conflict and LSCO, the US Army is woefully unprepared for the likely potential of epidemic disease in the operational environment. The DoD Military Health System’s force health protection mission considers factors of the operational environment that influence the health of the force—to include endemic diseases. Medical intelligence components such as the Armed Forces Health Surveillance Branch and the National Center for Medical Intelligence both have an important role to play in anticipating pathogenic threats to the force. However, in relying on these current structures and capabilities, the US military is in danger of repeating the mistakes that allowed it to be surprised by the diseases of the Second World War. The current organizations are geared to understand the spread of disease in the current operational environment. It is unlikely that either have sufficient resources to predict and rapidly communicate how changes made to the environment during a rapidly moving LSCO will affect the picture. Even if they had, they are not well integrated with the maneuver elements of the force.

The responsibility for planning for disease casualties cannot rely on the Military Health System and medical intelligence organizations alone. Given the losses and problems posed by epidemics in war, planning for them at the operational level must be part of the responsibility of all commanders. They must learn whether there are areas in which to avoid committing certain types of forces or, at the very least, anticipate the types of effects disease may have on their forces. In order to facilitate this, commanders must understand how their forces’ actions will impact the pathogenic terrain. This means at the bare minimum both exercises in professional military education and exercises for division-level echelons and above need to include epidemics and historically based levels of disease non-battle casualties. The various medical intelligence and planning bodies must be resourced and included in all such exercises so that commanders know where to go for assistance and information.

Thinking about the effect of disease on the force, while imperfect in execution, was once common for US Army commanders and, if the US Army is to prevail in great-power conflict, it must become so again. Given the increased lethality anticipated in future great-power conflict and the trends in emerging disease, the Army can little afford to fail in this critical aspect of preparation.


Dr. Jacob Stoil is a military historian and currently Assistant Professor of Military History at the US Army School of Advanced Military Studies. He received his doctorate in history from University of Oxford. He holds a BA in War Studies as well as an MA in History of Warfare from the Department of War Studies at King’s College London. He has published on indigenous force cooperation, the Second World War, and the Israeli military. Dr. Stoil is an Assistant Director of the Second World War Research Group, North America. He can be reached on twitter at @JacobStoil.

Maj. Bethany Landeck is a student in the Advanced Military Studies Program at the School of Advanced Military Studies at Ft Leavenworth, Kansas. Her most recent assignment was as Battalion Executive Officer for 21st Combat Support Hospital and 9th Hospital Center, Fort Hood, Texas. Bethany has deployed in support of Operation Enduring Freedom. She has a bachelor’s degree in General Health Science from Purdue University, where she earned her commission through the ROTC program.

The views expressed are those of the author and do not reflect the official position of the United States Military Academy, US Army Command and General Staff College, Department of the Army, Department of Defense, or any other government agency. (References to this article should include the foregoing statement.)


Image credit: Sgt. Amber I. Smith, US Army