The U.S. Army has long been leery of cities. Too often, urban warfare has meant heavy casualties, mass destruction and an enormous commitment of time and resources. In cities, enemy forces have more places to hide, and superior U.S. technology becomes less effective.“Dense urban terrain favors the defender,” said Col. Kevin Felix, chief of the Future Warfare Division at the Army Capabilities Integration Center. That’s why “in the past, in the central plains of Europe, you would fix and bypass a city,” he said.The world is changing, though, and that doctrine is being re-examined. The Army has become convinced that urban combat soon will be unavoidable, and when it happens, it will occur on a scale that the Army has never experienced. The reason? Megacities, or cities with a population of 10 million or more.“Worldwide, an historic transition is underway. Over half of all people currently live in cities, and the rate of migration is accelerating,” the Army Strategic Studies Group said in a 2014 report, Megacities and the United States Army. “Each day, an estimated 180,000 people across the globe migrate to cities,” the report said. “By 2030, cities will account for 60 percent of the world’s population and 70 percent of the world’s GDP [gross domestic product].”To the Army, that looks like trouble. “Megacities are rapidly becoming the epicenters of human activity on the planet and, as such, they will generate most of the friction which compels future military intervention,” the report said.Familiar GroundUrban warfare is not new for the Army. From the building-by-building and block-by-block battle for Aachen, Germany, in 1944 to the battles of Hue, Vietnam, in 1968 and Mogadishu, Somalia, in 1993, the Army has done plenty of fighting in cities.For much of a decade, U.S. soldiers fought Shiite militiamen in Baghdad’s teeming Sadr City slum and Sunni insurgents elsewhere in the city. Baghdad is not a megacity, but it probably offers the best example so far of what U.S. military operations will be like in one, said Daniel Rothenberg, co-director of the Center on the Future of War at Arizona State University.Despite maintaining a massive presence in Baghdad for years, the U.S. military was never able to ensure security. “You had complete technological military dominance. You had air power and incredibly well-armed, well-trained U.S. troops, but when they encountered the complexities of urban warfare, they were unable to control it,” Rothenberg said.During the U.S. occupation from 2003 to 2011, Baghdad was wracked by car bombings, suicide bombings, roadside bombs, rocket and mortar attacks, and assassinations. “One in four Iraqis fled their homes when we were there,” Rothenberg said. “Compare that to the clear military successes of Desert Storm.” During that 1991 campaign, U.S. forces fighting in the wide open desert “were able to take out an army’s worth of tanks. It was the exact opposite of fighting in cities,” Rothenberg said. In the desert, there was no civilian population to get in the way and few places for the enemy to hide.Megacity ChallengesThe rise of megacities creates “all kinds of challenges” for the Army, Rothenberg said.The Strategic Studies Group warned that the battles in Baghdad were “small in comparison to the challenges ahead.” By 2030, the group’s report said, there will be 37 cities that are two to four times bigger than Baghdad.Many—likely most—megacities won’t be a problem for the Army. New York, Tokyo, London and Beijing will no doubt remain stable, thriving economic and cultural centers. Other megacities, however, will struggle, choked by overcrowding, pollution, poverty, crime and ethnic strife.For many residents of those megacities, basic necessities will be scarce. Drinkable water, electricity and housing will be in short supply. Medical care will be sporadic and food supplies inadequate. “Many emerging megacities are ill-prepared to accommodate the kind of explosive growth they are experiencing,” according to the report.Governing will be difficult as gangs, criminals and rival militias carve out their own territories and challenge municipal authorities. Stark inequality between the rich and the poor, and racial, ethnic and cultural differences will all contribute to instability.It is happening already in some megacities. In São Paulo, Brazil, some 30,000 millionaires travel by helicopter and armored car to avoid contact with the more than 3 million others who live in the city’s 1,600 poverty-stricken shantytowns. “The proximity of extreme wealth and poverty in this city has generated instability,” the report said. The city’s drug gangs pose another threat. In May 2006, they launched hundreds of attacks on public buildings and transportation, and since then they have killed scores of police officers.Or consider Lagos, Nigeria. Already 21 million strong, it is one of the world’s fastest-growing cities, and more than half of its population lives in grinding poverty.“If Lagos experienced a major natural disaster, or significant social unrest because of Lagos’ glaring wealth disparity, it’s unlikely that the extant security forces would be able to deal with the situation,” the Strategic Studies Group report warned. “This increases the likelihood that foreign assistance would be required, and considering America’s significant economic stake in Nigeria, some U.S. military assistance might be offered.”“Megacities are blind spots from which a strategic surprise could emerge. It is plausible that the Army could be called to act in one of these places tomorrow,” the report said. “And currently the Army is ill-prepared to do so.”Some equipment and technology that give the Army its margin of superiority on today’s battlefields won’t be as effective in megacities. Tanks and armored vehicles will have trouble negotiating cramped streets and alleys. Long-range weapons and sensors designed to detect enemies at a distance will be less useful in close urban quarters. Surveillance drones won’t be able to see insurgents hiding in buildings or in underground tunnels. Helicopters will be vulnerable to shoulder-fired missiles and rocket-propelled grenades. Artillery will kill too many civilians to be a viable weapon. And logistics—getting food, medicine and other supplies in and casualties out—will be problematic, said Ben FitzGerald, director of the Technology and National Security Program at Center for a New American Security.‘The Great Leveler’“Urban combat is the great leveler,” David Shunk, a researcher at the Army’s Future Warfare Division, wrote in 2014 in Small Wars Journal. “Standoff technologies are negated and the city fight is still street to street, floor to floor, and often face to face.”“Tactically, a city’s closely packed buildings, basements, alleyways and sewer systems offer cover, concealment, and ready-made defensive positions to the defenders. Generally, a modern city magnifies the power of the defender and robs the attacker of his advantages in firepower and mobility,” Shunk said.Cellphone networks, the Internet and social media will provide the communication insurgents need to rally supporters and coordinate attacks. Google maps and GPS will help them more accurately target U.S. forces. Such readily available commercial technology will “help even out the fight,” FitzGerald said.By around 2030, technology will be much more advanced, Shunk said. Capabilities including “improved UAVs [unmanned aerial vehicles], 3-D printing, and robotics will greatly empower the adversaries.” Warlords and drug gangs may have their own drone fleets, cyber weapons and increasingly sophisticated improvised explosive devices.“A city can ingest an invading army, paralyze it for weeks on end, and grind it down to a state of ineffectiveness,” Shunk warned, quoting Christopher R. Gabel in Combined Arms in Battle Since 1939, released by the U.S. Army Command and General Staff College in 1992.Felix, of the Future Warfare Division, calls that “the tyranny of scale.” Megacities are gigantic. “You can’t just pour brigade after brigade into a megacity. They’ll just get swallowed up,” he said after a megacity war game last August.So why would the Army even consider fighting in a megacity?It shouldn’t, said Daniel Goure, vice president of the Lexington Institute, a national security think tank. The Army is in the midst of “a massive rethink” about its future, “and it looked out there and said, ‘Oh my God, massive urbanization is going on and there is instability out there, so we have to go in.’ That doesn’t follow. What size army would you need to seize control of, police and maintain order in a city of 30 million?” The entire U.S. Army “couldn’t control Cairo if the city was in chaos,” he said. Greater Cairo has a population of 22 million.Alternate AvenuesInstead of planning to wage wars in megacities, the Army should be developing techniques to deal with trouble in megacities by other means, Goure said. By perfecting its ability to conduct lightning raids, for example, the Army could enter a megacity suddenly, solve a problem such as stopping missiles from being fired from within the city, and exit quickly to avoid getting bogged down.In the event of “a massive humanitarian crisis, maybe we can send the Army in,” but if the crisis devolves into combat, it is time to get out, Goure said. Rather than fight, the Army could “cut off water, cut off food, lay siege to it and call it a day.” Civilians would be hurt by a siege but perhaps less than they would be hurt by urban warfare.The Strategic Studies Group dismissed the idea that sieges would work on megacities and said combat in the cities seems inevitable. “It is highly likely that megacities will be the strategic key terrain in any future crisis that requires U.S. military intervention,” the group wrote.If a megacity becomes a “safe haven for threat groups who wish to strike the U.S. home land,” the Army might be obliged to intervene, the group said. The U.S. Army might also have to act “if internal or foreign actors conducted offensive operations” that threaten to topple the government of an ally.The Army can’t simply declare megacities off-limits, Felix said. “The key thing is: The Army is about creating options for the president and the national command authority,” so the Army must be prepared to offer “multiple options related to multiple dilemmas across multiple domains,” from disaster response to countering weapons of mass destruction, he said. “That’s our goal.”So far, however, the options for dealing with megacities aren’t obvious. “We learned quite a bit over the last 14 years” while fighting in Iraq and Afghanistan, Felix said, but mega-cities are different. “The scope and the scale of this are beyond what we have done in the past.”The Strategic Studies Group put it bluntly: “The Army is currently unprepared. Although the Army has a long history of urban fighting, it has never dealt with an environment so complex and beyond the scope of its resources. A decade of war in Iraq and Afghanistan has taught the Army that it must shape itself to the complex environments in which it is called to operate. This is the process that must begin now with megacities.”Creating InroadsAs it reshapes, the Army needs new approaches to training, new doctrine and new technology, Felix said. “Training at the JRTC [Joint Readiness Training Center at Fort Polk, La.] and the NTC [National Training Center at Fort Irwin, Calif.] does not replicate the scope and scale” of what soldiers will face in megacities, he said.Alternatives? The Army is already sending some soldiers to New York City to “talk to emergency management folks and learn from them,” Felix said. The Army should also “go to cities with multiple actors”—criminal gangs, militias and nonstate insurgents—and find out how police and other authorities deal with them.The Army also must overhaul training for its leaders, putting greater “emphasis on adaptability, resilience and agility,” Felix said. Potential leaders must be given “a lot of broadening assignments” with “a tremendous emphasis on higher education.” Fellowships in academic institutions or megacity emergency management centers should become a standard part of leadership training, he said.Soldiers must develop a good understanding of “all the tribes and the cultures” that contribute to unrest in particular megacities, Felix said. “We will not be able to show up and sort that out in a crisis.” Regionally aligned forces that focus on specific geographic areas could compile and maintain that knowledge base, he said.Here’s another worry: The Army is shrinking. From its peak of 570,000 soldiers in 2010, the Army is headed to 490,000 by 2017 and maybe fewer after that. In addition, more of the Army will be based in the U.S. A force that is both smaller and more U.S.-based will make expeditionary operations a bigger challenge, Felix said.Hope in TechnologyNevertheless, technology offers some hope. Advances in unmanned ground and air systems will boost Army reconnaissance and security capabilities, Felix said. 3-D printing may enable the Army to produce repair parts or even weapons on the battlefield. Synthetic biology could enable the Army to create vaccines in real time, he said, and alternative power sources could substantially reduce logistics tails (the supplies that accompany the Army in and out of an area). Army research labs are already working to identify and develop technology that soldiers will need to operate in megacities, Felix said.Autonomy—machines that can operate with minimal input from humans—could be a major benefit for U.S. forces in megacity operations, FitzGerald said. The Army should be developing robots “that do breaches and enter buildings so that the robot gets shot, not soldiers.”In dense urban environments, nonlethal weapons will also be necessary, Felix said, and cyber weapons—offensive and defensive—will probably become “a major element of operations.” Others are urging the development of laser weapons, swarming unmanned aerial vehicles and smaller but tougher armored vehicles.Megacities will call for “more ISR, lots of tactical ISR,” Goure said, referring to intelligence, surveillance and reconnaissance sensors, as well as “much more precision firepower,” communications equipment that’s designed to operate in urban canyons, more effective IED defeat systems and better close-combat weapons.Meanwhile, the Army’s urban warfare doctrine needs to be rewritten, the Strategic Studies Group said. Attempting to isolate a megacity by controlling its perimeter won’t work. “Physically controlling an urban population consisting of tens of millions of people spread over hundreds of square miles with military forces numbering in the tens of thousands” is unrealistic, the group said. In addition, “virtual isolation” is unlikely because of the vast connectivity available through cellphones and the Internet.“Ground maneuver from the periphery is also unrealistic,” the group went on to say. The combination of urban congestion and the enormous size of megacities “makes even getting to an objective from the periphery questionable, let alone achieving an operational effect,” the group said. “The scale of megacities, in essence, defies the military’s ability to apply historical methods.”How to deal with megacities remains a challenge, but as the nation’s primary force for operations on land, the Army “must take ownership of the megacity challenge,” the Strategic Studies Group said. “To ignore megacities is to ignore the future.”“We are constantly learning and adapting to this environment,” Felix said. “The Army will continue to think through this problem.”