We cannot know for certain what the future operating environment will be, but we must prepare for it. To date, the US military has not paid enough attention the rise of megacities. This article argues the US Army must continue developing new concepts, capabilities, and ultimately solutions for achieving national security objectives within the current and future operational environments of the megacity. ********** The 2014 Army Operating Concept (AOC) defines the term complex as environment that is not only unknown, but unknowable and constantly changing. (1) It goes on claim that to win in a complex world, Army forces must provide the Joint Force with multiple options, integrate the efforts of multiple partners, operate across multiple domains, and present enemies and adversaries with multiple dilemmas. (2) Nowhere is this more crucial or difficult accomplish than in the complex urban environment of a megacity. Such cities present the Army and joint force with a level of complexity for which they are not fully prepared. However, many opportunities exist for the Army and joint force reinvigorate past research efforts, consolidate learning, and prepare the current and future force for operations in such environments. Historical Context Urban warfare is not a new phenomenon. For example, in the ancient Syrian city of Hamoukar, archeologists have discovered evidence of urban combat as early as 5,500 years ago. (3) Throughout the ages, urban conflicts have tended be more the rule than the exception. Previous wars centered on the sieges and defense of urban centers of all sizes, while large battles have for centuries been the exception rather than the rule. Contemporary reminders of urban warfare and its inherent challenges include the battles of Stalingrad and Aachen during World War II, Hue during Vietnam, and Grozny in 1994-1995, and again 1999-2000. There is little reason believe future conflicts will not also require some form of urban warfare. As such, the Army's capacity engage, fight, and win major urban combat operations will determine the success of future operational and strategic endeavors. The Battle of Hue during the Vietnam conflict reflected the tendency for urban combat operations blend the levels of war, creating the situation where tactical outcomes had significant strategic implications. Arguably, the bloodiest battle during the Tet Offensive took place in Hue, Vietnam's third largest city, with significant operational, cultural, and spiritual significance. The Battle for Hue involved 26 days of intense street-to-street, house-to-house fighting against a determined enemy established in a defense-in-depth. Major urban combat operations occurred in the midst of a civilian population of around 140,000 people, and against an initial enemy force estimated at 7,500 North Vietnamese Army (NVA) and Viet Cong (VC) troops, later reinforced a division-sized element. Facing them were three US Marine battalions and 11 Army of the Republic of Vietnam (ARVN) battalions. (4) Although the United States employed Army units from the 1st Cavalry Division and 101st Airborne Division during the Battle of Hue, these forces focused on the outlying areas prevent NVA reinforcement. The US Marines and ARVN conducted the majority of fighting inside the city. When the fight for Hue ended, US and ARVN forces retook the city. The US military suffered 216 killed and 1,364 wounded, while the ARVN lost 384 killed and 1,830 wounded. Civilian casualties were around 5,800 people killed or executed by NVA/VC due their political allegiances. Estimated enemy casualties were 1,042 killed and 4,000 wounded. (5) Despite the tactical gains from retaking the city and repelling enemy forces across South Vietnam, the United States and Republic of Vietnam faced the strategic repercussions of having laid in ruins an estimated 80 percent of the city, with over 116,000 persons left homeless. …