Though North Korea has been a persistent U.S. foreign policy challenge for decades, during 2017 the situation evolved to become what many observers assess to be a potential direct security threat to the U.S. homeland. In July 2017, North Korea apparently successfully tested its first intercontinental ballistic missiles (ICBMs). Some observers assert that North Korea has, with these tests, demonstrated a capability of reaching the continental United States, although others contend that these tests have not yet in actuality proven that the DPRK has achieved intercontinental ranges with its missiles. Regardless, these developments, combined with the possibility that the regime in Pyongyang has miniaturized a nuclear weapon, suggest that North Korea could now be only one technical step—mastering reentry vehicle technology—away from being able to credibly threaten the continental United States with a nuclear weapon. Some estimates reportedly maintain that North Korea may be able to do so by sometime in 2018, suggesting that the window of opportunity for eliminating these capabilities without possible nuclear retaliation to the continental United States is closing. Combined with the long-standing use of aggressive rhetoric toward the United States by successive Kim regimes, these events appear to have fundamentally altered U.S. perceptions of the threat the Kim Jong-un regime poses, and have escalated the standoff on the Korean Peninsula to levels that have arguably not been seen since at least 1994. In the coming months, Congress may opt to play a greater role in shaping U.S. policy regarding North Korea, including consideration of the implications of possible U.S. actions to address it. The United States has long signaled its preference for resolving the situation with diplomacy, and has used economic pressure, in the form of unilateral and multinational economic sanctions, to create opportunities for those diplomatic efforts. Various Trump Administration statements suggest that a mixture of economic pressure and diplomacy remains the preferred policy tool. To a greater degree than their predecessors, however, Trump Administration officials have publicly emphasized that "all options are on the table," including the use of military force, to contend with the threat North Korea may pose to the United States and its allies. Consistent with the policies of prior Administrations, Trump Administration officials have also stated that the goal of their increased pressure campaign toward North Korea is denuclearization—the removal of nuclear weapons from the Korean Peninsula. If the Trump Administration chooses to pursue military options, key questions for Congress include whether, and how, to best employ the military to accomplish denuclearization, and whether using military force on its own or in combination with other tools might result in miscalculation on either side and lead to conflict escalation. Intended or inadvertent, reengaging in military hostilities in any form with North Korea is a proposition that involves military and political risk. Any move by the United States, South Korea, or North Korea could result in an unpredictable escalation of conflict and produce substantial casualty levels. A conflict itself, should it occur, would likely be significantly more complex and dangerous than any of the interventions the United States has undertaken since the end of the Cold War, including those in Iraq, Libya, and the Balkans. Some analysts contend, however, that the risk of allowing the Kim Jong-un regime to acquire a nuclear weapon capable of targeting the U.S. homeland is of even greater concern than the risks associated with the outbreak of war, especially given Pyongyang's long history of threats and aggressive action toward the United States and its allies and the regime's long-stated interest in unifying the Korean Peninsula on its terms. Some analysts assert that preemptive U.S. military action against North Korea should be taken when there is an "imminent launch" of a North Korean nuclear-armed ICBM aimed at the United States or its allies. Other analysts downplay the risk of North Korean nuclearization; few analysts believe that North Korea would launch an unprovoked attack on U.S. territory. Many students of the regional military balance contend that an overall advantage over North Korea rests with the United States and its ally, the Republic of Korea (or, ROK, commonly known as South Korea), and that U.S./ROK forces would likely prevail in any conflict within a matter of weeks. Those analyses, however, also generally assume that neither China nor Russia would become engaged in the conflict. Should China or Russia do so, the conflict would likely become significantly more complicated, costly, and lengthy. The toll of such a conflict could be immense, given that Seoul—with a population of approximately 23 million people, including American citizens—is within the range of North Korean artillery deployed near the demilitarized zone (DMZ) between the two Koreas. Should the DPRK use the nuclear, chemical, or biological weapons in its arsenal, according to some estimates casualty figures could number in the millions. Depending upon the nature of the conflict and the strategic objectives being advanced, U.S. military casualties could also be considerable. As a result, Congress may consider whether to support increased U.S. military activities—possibly including combat operations—to denuclearize the Korean peninsula, or whether instead to support efforts to contain and deter North Korean aggression primarily through other means. Any option would carry with it considerable risk to the United States, the region, and global order. As Congress considers these issues, key strategic-level questions include, but are not limited to, the following: Could the North Korean regime change its calculus, or collapse or otherwise transform, perhaps as a result of outside pressure, prior to its acquisition, or use, of credible nuclear-tipped ICBMs capable of holding targets in the continental United States at risk? What are the implications for U.S. relationships in the region if key allies are persuaded that the United States will no longer give the priority to regional security that it has thus far? What will be the cost implications, in terms of U.S. and allied financial resources, casualties, standing, and reputation, should hostilities break out, and how would those costs affect the ability of the United States to advance other critical national security objectives in other theaters? How do the risks associated with U.S. military action against North Korea compare with the risks of adopting other strategies, such as deterring and containing North Korea? Would a nuclear-armed Kim regime behave in a manner consistent with other nuclear powers? What would a nuclear-armed North Korea mean for longer-term national security decisions the United States faces? U.S. officials have been concerned about the threats North Korea poses to international order and regional alliances since Pyongyang's 1950 invasion of South Korea. The United Nations Security Council authorized a 16-nation Joint Command, of which the United States was a significant participant, to intervene on the Korean Peninsula to help repel North Korean forces. Shortly thereafter, when U.S. and allied forces pushed far into North Korean territory, China deployed its armed forces to assist the North. The parties eventually fought back to the 38 th parallel that originally divided the peninsula following World War II. Counts of the dead and wounded vary: according to the U.S. Department of Defense, more than 33,000 U.S. troops were killed and over 100,000 were wounded during the three-year-long Korean War; China lost upwards of 400,000 troops, with an additional 486,000 wounded; and North Korea's armed forces dead numbered around 215,000, with some 303,000 wounded. South Korea witnessed an estimated 138,000 armed forces and 374,000 civilians killed. Hostilities were formally suspended in 1953 with the signing of an armistice agreement rather than a peace treaty. Over the subsequent decades, the United States and its regional allies have largely contained the military threats to U.S. interests in Northeast Asia posed by North Korea. The United States and its ally South Korea have deterred three generations of the ruling Kim dynasty in Pyongyang from launching large-scale military operations. The U.S. security commitment to, and relationship with, the Republic of Korea has helped South Korea to emerge as one of the world's largest industrialized countries and, since the late 1980s, a flourishing democracy. South Korea today is one of the United States' most important economic and diplomatic partners in East Asia and globally. With respect to the Korean Peninsula itself, two key components of U.S. policy have been the U.S.-ROK Mutual Defense Treaty, along with the presence of some 28,500 U.S. troops in South Korea. Congress has supported the overall U.S. security approach to Northeast Asia, with the Senate approving defense treaties (and their revisions) with South Korea and Japan, and Congress providing funding for and oversight of the forward deployment of U.S. troops in both countries. U.S./ROK efforts, however, along with those of other countries, have to date failed to compel the DPRK to abandon its nuclear weapons and ICBM programs. Since Pyongyang began undertaking its weapons of mass destruction (WMD) acquisition programs in earnest in the 1980s, the United States and the international community writ large have employed a range of tools, including diplomacy, sanctions, strengthening of the capabilities of U.S. political and military alliances, and attempts to convince China to increase pressure on the DPRK to change its behavior. Around 90% of North Korea's trade is with China, which arguably gives Beijing significant leverage over Pyongyang. Some argue that these efforts have slowed but not stopped North Korea's drive toward developing a nuclear ICBM capability. The Trump Administration, as did the Obama Administration before it, places significant emphasis on expanding economic and diplomatic sanctions on North Korea and third-party entities that deal with North Korea. At the U.N. Security Council, the United States led efforts to pass eight sanctions resolutions, including the most recent, Resolution 2375, which was adopted in September 2017. For its part, Congress enacted the North Korea Sanctions and Policy Enhancement Act of 2016 (NKSPEA, P.L. 114-122 ; signed into law by President Obama in February 2016) and the Korean Interdiction and Modernization of Sanctions Act (KIMS Act, title III of P.L. 115-44 ; signed into law by President Trump in August 2017) to strengthen actions already taken by the executive branch to implement sanctions required by the Security Council and to expand those economic activities in which North Korea engages that could be subject to penalties—including trade and transactions with third countries (secondary sanctions). Further, since the George H. W. Bush Administration, the United States has imposed unilateral measures against North Korean entities, and entities in third countries, found to have been instrumental in North Korea's WMD programs. To implement the NKSPEA and KIMS Acts, the United States has also imposed economic sanctions on entities in China and Russia for activities that allegedly provide revenue to the North Korean government, provide the means to evade sanctions, or boost the regime's ability to advance its WMD capabilities. The United States also has worked to strengthen the military capabilities of South Korea and Japan. Two key diplomatic efforts have aimed to induce North Korea to abandon its nuclear weapons program: the Agreed Framework (1994-2002) and the Six-Party Talks (2005-2009). The Agreed Framework between the United States and North Korea followed a ratcheting up of tensions that nearly led to a U.S. military strike. The Six-Party Talks, which involved the DPRK, China, Japan, Russia, South Korea, and the United States, ran from 2003 to 2009, a period that included the first North Korean nuclear test in 2006. During both sets of negotiations, in exchange for specific economic and diplomatic gains, North Korea committed to eventual denuclearization, froze nuclear material production, and partially dismantled key facilities. Since withdrawing from the Six-Party Talks in 2009, North Korea has not agreed to return to its past denuclearization pledges. Subsequently, the United States has primarily concentrated its diplomatic efforts on convincing other nations to increase economic pressure to implement U.N. Security Council resolutions more fully. North Korea watchers argue that the ruling elite's fundamental priority is the survival of the Kim regime. For this reason, few analysts believe that North Korea would launch an unprovoked attack on U.S. territory or U.S. overseas bases; the consequences for doing so could include a possible overwhelming U.S. military response that could result in the end of the Kim Jong-un regime, and possibly the end of the DPRK as a sovereign state. The National Intelligence Manager for East Asia responsible for integrating the intelligence community's analysis said in a June speech that We believe North Korea's strategic objective is the development of a credible nuclear deterrent. Kim Jong Un is committed to development of a long range nuclear armed missile capable of posing a direct threat to the continental United States to complement his existing ability to threaten the region. Kim views nuclear weapons as a key component of regime survival and a deterrent against outside threats. Kim probably judges that once he can strike the U.S. mainland, he can deter attacks on his regime and perhaps coerce Washington into policy decisions that benefit Pyongyang and upset regional alliances—possibly even to attempt to press for the removal of U.S. forces from the peninsula. North Korea has itself repeatedly emphasized the role of its nuclear weapons as an added deterrent to attack by the United States and/or South Korea. On October 20, 2017, North Korean Foreign Ministry official Choe Son Hui reiterated her government's past statements that its nuclear arsenal is meant to deter attack from the United States and that keeping its weapons is "a matter of life and death for us." She also said that "the current situation deepens our understanding that we need nuclear weapons to repel a potential attack." Under Kim Jong-un, North Korea pursues an official policy of byu ngjin —simultaneous development of its nuclear weapons and its economy. On April 1, 2013, North Korea's party congress adopted the "Law on Consolidating Position of Nuclear Weapons State." The official media (KCNA) summarized the law as saying that nuclear weapons "serve the purpose of deterring and repelling the aggression and attack of the enemy against the DPRK and dealing deadly retaliatory blows at the strongholds of aggression until the world is denuclearized." Many analysts are concerned that North Korea could launch an attack first, even with nuclear-armed missiles, if it perceived a U.S. attack as imminent. These voices emphasize the need for careful U.S. rhetoric and confidence-building measures to avoid miscalculation. The Director of National Intelligence said in early 2012 that "we also assess, albeit with low confidence, Pyongyang probably would not attempt to use nuclear weapons against US forces or territory, unless it perceived its regime to be on the verge of military defeat and risked an irretrievable loss of control." Possessing nuclear weapons and long-range missile capability could also help the Kim government achieve a number of additional long-standing objectives. In May 2017 testimony, Director of National Intelligence Dan Coats repeated the intelligence community's long-standing analysis that, "Pyongyang's nuclear capabilities are intended for deterrence, international prestige, and coercive diplomacy." Accordingly, Pyongyang may also see the acquisition of a nuclear-tipped ICBM capability as a way to increase its freedom of action, in the belief that the United States will be more constrained if North Korea can credibly threaten U.S. territories. The DPRK may believe that by acquiring nuclear-tipped ICBM capability, and thereby deterring the United States, it might have a greater chance of achieving its ultimate goal of reunifying the Korean Peninsula. Important steps in this process would include weakening the credibility of the U.S. commitment to defend South Korea and persuading the United States to remove sanctions and withdraw its troops from the Korean Peninsula. North Korea may also see recognition as a nuclear weapons state as a way to cement its legitimacy, both with its own populace and with the international community. Sanctions, diplomacy, interdiction, and military capacity-building efforts have arguably slowed—for instance, through raising the costs of procuring materials—although not halted, the advance of North Korea's WMD programs. As multinational sanctions have gained momentum during the past several years, however, DPRK progress in its missile programs has also significantly accelerated. As a result of this progress, the Trump Administration appears to have raised the issue of North Korea's nuclear and missile programs to a top U.S. foreign and national security policy priority. Describing its policy as "maximum pressure," or "strategic accountability," the Administration has adopted an approach of increasing pressure on Pyongyang in an effort to convince the North Korean regime "to de-escalate and return to the path of dialogue." In August 2017, Secretary of State Rex Tillerson and Secretary of Defense James Mattis outlined the U.S. policy objective and parameters for the Korean Peninsula: The object of our peaceful pressure campaign is the denuclearization of the Korean Peninsula. The U.S. has no interest in regime change or accelerated reunification of Korea. We do not seek an excuse to garrison U.S. troops north of the Demilitarized Zone. We have no desire to inflict harm on the long-suffering North Korean people, who are distinct from the hostile regime in Pyongyang. In their public remarks, Trump Administration officials have emphasized that, while diplomacy and pressure will continue, a full range of military options could be employed to resolve the crisis. Chairman of the Joint Chiefs of Staff General Joseph Dunford, for example, stated at the Aspen Security Forum in July 2017 that "it is not unimaginable to have military options to respond to North Korean nuclear capability. What's unimaginable to me is allowing a capability that would allow a nuclear weapon to land in Denver, Colorado. That's unimaginable to me. So my job will be to develop military options to make sure that doesn't happen." A key factor driving the Administration's actions and statements appears to be the assessment that sometime in 2018, North Korea is likely to acquire the capability of reaching the continental United States with a nuclear-tipped ICBM. This assessment implies that the time frame for conducting military action without the risk of a North Korean nuclear attack against U.S. territory is narrowing. Such an assessment may increase the urgency of efforts to restart multilateral diplomatic efforts with North Korea, efforts that some maintain could be strengthened and accelerated if both North Korea and China believe that a U.S. military strike on the Korean Peninsula is becoming more likely. In addition to possible threats to the continental United States, allies, and U.S. Armed Forces in the region, concerns persist that should the goal of denuclearization remain unaccomplished, North Korea might continue to proliferate its missile and nuclear technology for a variety of reasons, including financial profit by selling materials and information to state and nonstate actors, joint exchange of data to develop its own systems with other states (Iran and Syria, most notably), or as part of a general provocative trend. DNI Dan Coats testified before Congress in May 2017 that "North Korea's export of ballistic missiles and associated materials to several countries, including Iran and Syria, and its assistance to Syria's construction of a nuclear reactor, destroyed in 2007, illustrate its willingness to proliferate dangerous technologies." In the wake of an earlier set of sanctions, former DNI Dennis Blair said in March 2016 that North Korea had "more motivation to increase their supply of hard currency any way they can," and selling nuclear materials was "certainly a possibility that has occurred to them." Some contend that the military is an inappropriate instrument for resolving the standoff between the DPRK and the international community. They argue, for example, that even the threat of military force actually strengthens the Kim regime domestically, as it feeds the DPRK narrative that it must be vigilant against an aggressive United States. These observers contend that, instead, the United States should focus its efforts on influence operations, in particular, to shape the perceptions of the Kim regime's mid-level leaders and the North Korean population. Doing so might, in turn, eventually foster the collapse of the Kim regime itself and possibly create a window for denuclearization of North Korea. Others, however, maintain that these kinds of influence operations are unlikely to affect North Korean society in a manner that might result in regime degradation or collapse. In addition, some observers argue that although denuclearization may be a long-term strategic goal of the United States, achieving this goal in the short term may be difficult, particularly due to the high risk of military escalation. Therefore, they maintain, other tactics, such as deterrence and containment, may be more appropriate than a preventive military strike. In addition, some see military pressure as well as sanctions as a way to raise the costs for North Korea of continuing on its current nuclear and missile development path, thereby persuading the DPRK to eventually agree to a halt or reversal in these programs. Understanding the military dimensions of the current standoff, and the relative feasibility of different options to use force to resolve the crisis, requires an appreciation of the extant military capabilities on the Korean Peninsula. Estimating the military balance in the region, however, and how military forces might be employed during wartime, requires accounting for a variety of variables; therefore, such estimation is an inherently imprecise endeavor. As an overall approach to designing its military, the DPRK has emphasized quantity over quality, and has committed considerable resources to developing asymmetric capabilities such as weapons of mass destruction and Special Operations Forces. The Republic of Korea, by contrast, has emphasized quality over quantity and maintains a highly skilled, well-trained, and capable conventional force. In terms of cyber capabilities, the DPRK has been conducting increasingly aggressive cyber operations against the heavily networked ROK and other targets. Although the DPRK has limited Internet connectivity itself, components of its weapons programs may be vulnerable to cyberattacks. Appendix A analyzes in detail the capabilities of the key actors presently on the Korean Peninsula. The Korean People's Army (KPA)—a large, ground force-centric organization comprising ground, air, naval, missile, and special operations forces (SOF)—has over 1 million soldiers in its ranks. Although it is the fourth-largest military in the world, it has some significant deficiencies, particularly with respect to training and aging (if not archaic) equipment. A number of analysts attribute that degradation of capability to food and fuel shortages, economic hardship, and an inability to replace aging equipment, because of international arms markets being closed to North Korea due to sanctions and international nonproliferation regimes, among other factors. To compensate, particularly in recent years, the DPRK appears to have heavily invested in asymmetric capabilities, both on the "high" (for example, weapons of mass destruction) and "low" (for example, SOF) ends of the capability spectrum. The presence of chemical and biological weapons that could reach South Korea and parts of Japan has long been confirmed; some observers believe that those systems would be immediately employed by the DPRK regime in the event of a conflict. Hardened facilities, particularly in forward locations, are thought to protect artillery and supplies and WMD capabilities, including chemical munitions. The DPRK also has missiles believed capable of reaching Guam, other U.S. bases, and allies in the immediate region, including Japan. With respect to the "low" end of the capability spectrum, estimates vary on the size of DPRK SOF, although U.S. and ROK intelligence and military sources reportedly maintain that its end strength may be as high as 200,000, including 140,000 light infantry and 60,000 in the 11 th Storm Corps. These "high" and "low" capabilities are in addition to the considerable DPRK inventory of long-range rockets, artillery, short-range ballistic missiles, and chemical weaponry aimed at targets in the Republic of Korea. U.S. military facilities and the Seoul region, the latter with a population of approximately 23 million, are within range of significant conventional artillery capabilities situated along the DMZ. Reports indicate that the DPRK has enhanced the mobility of its missile launchers and at least some of its artillery batteries, arguably making them more difficult to target. Reports also suggest that the DPRK has hardened many of its key facilities through an extensive network of underground tunnels, a further challenge to fully identifying the DPRK's military capabilities. While the DPRK has sought to balance its conventional deficiencies with asymmetric capabilities, the Republic of Korea has steadily improved its conventional forces, through increasing their lethality with improvements in command, control, and communications and advanced technology, as well as through incorporating battlefield lessons from its experience in Operation Iraqi Freedom. Still, the ROK's active duty military is approximately half the size of the DPRK's, leading some analysts to conclude that South Korea may not be able to amass enough force to meet a challenge from the North. ROK leaders have decided not to acquire nuclear weapons, but rely instead on U.S. security assurances (in particular, the U.S. extended deterrent nuclear umbrella). Toward that end, some in South Korea, in particular, the Liberty Korea Party, have called for the redeployment of U.S. tactical nuclear weapons in order to send a powerful deterrent message to the North and demonstrate a strong commitment to the South. ROK became a signatory to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in 1975 and is a state party to other related treaties and nonproliferation regimes, including those curtailing chemical and biological weapons and missile proliferation. There are 28,500 U.S. troops and their families currently stationed in the Republic of Korea, primarily playing a deterrent role by acting as a tripwire in case of DPRK hostilities south of the DMZ. U.S. Armed Forces train with their ROK partners to better prepare them to participate in coalition operations. The United States reportedly also provides the ROK with several key enablers, including military intelligence. Since 2004, the U.S. Air Force has increased its presence in ROK through the regular rotation into South Korea of advanced strike aircraft. These rotations do not constitute a permanent presence, but the aircraft often remain in South Korea for weeks and sometimes months for training. Due to these conventional capabilities, as well as the U.S.-ROK Mutual Defense Treaty, the United States has extended its deterrent umbrella to South Korea, including nuclear deterrence. Under current U.S./ROK operational plans (OPLANS), the South Korean government has publicly stated that the United States would deploy units to reinforce the ROK in the event of military hostilities. In the event of wartime, and depending on those circumstances, official ROK sources note that up to 690,000 additional U.S. forces could be called upon to reinforce U.S./ROK positions, along with 160 naval vessels and 2,000 aircraft. As one observer notes, due to the complexity of the situation and the different military capabilities of all sides, predictions regarding how hostilities might unfold on the Korean Peninsula are comparable to describing a "very complex game of three-dimensional chess in terms of tic-tac-toe." Accordingly, rather than analyzing possible DPRK countermoves or possible military campaign trajectories, this section briefly discusses some key risk considerations related to possible military action on the Korean Peninsula. The Kim regime could respond to any kind of U.S./ROK military activity through a variety of conventional and unconventional means, any use of which could escalate into a full-scale war on the Korean Peninsula. Detailing specific possible responses is difficult, however, given the scarcity of relevant available literature. In the first instance, despite noted deficiencies in its overall conventional force structure, many observers expect the DPRK would employ its conventional artillery toward targets in South Korea and inflict considerable damage upon Seoul (as detailed in the next section). In terms of unconventional responses, the DPRK might employ its highly trained SOF to sabotage U.S./ROK targets south of the DMZ. The DPRK might also employ weapons of mass destruction during a conflict with the U.S./ROK. A possibility also exists that a conflict with DPRK could escalate into nuclear warfare, the result of which could be radioactive contamination that could affect all states in the immediate region, including China, Japan, and South Korea. As a consequence in this possible contingency, U.S. forces would likely be required to operate in WMD-contaminated zones, and the Korean Peninsula itself could face enormous devastation and loss of life. North Korea also could launch a cyberattack against the United States, South Korea, or other targets. Further, some observers contend that North Korea may already have the capability to launch a nuclear attack against the continental United States, possibly delivered covertly by smuggling, or even through using container ships as a means of delivery. Figure 2 depicts population density on the Korean Peninsula. It suggests that an escalation of a military conflict on the peninsula could affect upwards of 25 million people on either side of the border, including at least 100,000 U.S. citizens (some estimates range as high as 500,000). Even if the DPRK uses only its conventional munitions (which most analysts believe would be unlikely given North Korea's arsenal of WMD capabilities), some estimates range from between 30,000 and 300,000 dead in the first days of fighting, given that DPRK artillery is thought by some to be capable of firing 10,000 rounds per minute at Seoul. Casualties would likely be significantly higher should nonconventional munitions or capabilities be used. This wide range of casualty estimates is due to the fact that a wide variety of variables (including campaign length, weaponry used, the effectiveness of noncombatant evacuation operations, whether China or Russia might become militarily involved and so on) would likely have significant bearing on the actual numbers of casualties on all sides. Responding to congressional inquiries, the Joint Staff released a letter on October 27, 2017, noting the difficulty of accounting for these variables when projecting civilian casualties in the event of a resumption of hostilities on the Korean peninsula . Still, as one observer states Estimates are that hundreds of thousands of South Koreans would die in the first few hours of combat—from artillery, from rockets, from short range missiles—and if this war would escalate to the nuclear level, then you are looking at tens of millions of casualties and the destruction of the eleventh largest economy in the world. Pyongyang could also escalate to attacking Japan with ballistic missiles. Japan is densely populated, with heavy concentrations of civilians in cities: the greater Tokyo area alone has a population of about 38 million. The regime might see such an attack as justified by its historic hostility toward Japan based on Japan's annexation of the Korean Peninsula from 1910 to 1945, or it could launch missiles in an attempt to knock out U.S. military assets stationed on the archipelago. A further planning consideration is that North Korea might also strike U.S. bases in Japan (or South Korea) first, possibly with nuclear weapons, to deter military action by U.S./ROK forces. When discussing the possibility of renewed hostilities on the Korean Peninsula, Secretary of Defense James Mattis stated that although the United States would likely prevail in a military campaign against the DPRK, it "would be probably the worst kind of fighting in most people's lifetimes." The possibly extraordinary loss of life presents other complicating factors to the prosecution of military operations on the Korean Peninsula. Evacuating surviving American noncombatants (noncombatant evacuation operations, or NEOs), including families of U.S. military stationed there, could place a further strain on U.S. military capabilities in theater, and could complicate the flow of additional reinforcements from the continental United States. Medical facilities could be overwhelmed handling civilian casualties—which, as noted above, might involve treating exposure to chemical if not biological or nuclear weapons—making it more difficult to treat military casualties. The impact of renewed hostilities on the South Korean, regional, and global economies, especially should hostilities escalate into a full-scale war, would likely be substantial. According to one rough estimate by a 2010 RAND study, the costs of a conventional war could amount to 60%-70% of South Korea's annual GDP, which in 2016 was $1.4 trillion. The study estimated that if North Korea detonated a 10 kt nuclear weapon in Seoul, the financial costs would be more than 10% of South Korea's GDP over the ensuing 10 years. These figures should be treated as a rough order of magnitude rather than a precise costing estimate. Given the DPRK's impoverished state, ROK reconstruction costs might also be affected by the costs of rehabilitating the North Korean economy. A significant factor likely affecting policymakers' deliberations regarding the use of military force on the Korean Peninsula is the question of whether a military conflict between the DPRK and the U.S./ROK runs the risk of a direct military clash with China, as occurred during the 1950-1953 Korean War. China has declared itself "firmly opposed to war and turmoil on the Peninsula," and "committed to a denuclearized, peaceful and stable Korean Peninsula and a settlement of relevant issues through dialogue and consultation." If the United States were to undertake preventive or preemptive strikes against North Korea, it could risk a major rupture in its relationship with China, which is the United States' top trading partner and holds upwards of $1.15 trillion in U.S. bonds as of June 2017. In August 2017, the Global Times , a nonauthoritative tabloid affiliated with the authoritative Chinese Communist Party publication The People's Daily , wrote in a much-discussed editorial that China should also make clear that if North Korea launches missiles that threaten U.S. soil first and the U.S. retaliates, China will stay neutral.... If the U.S. and South Korea carry out strikes and try to overthrow the North Korean regime and change the political pattern of the Korean peninsula, China will prevent them from doing so. China's leadership has been known to use the Global Times to test policy proposals and messages while taking advantage of the deniability offered by the paper's nonauthoritative status. Whether this editorial was a test message from China's leadership, or generated independently by the Global Times , is unclear. China increasingly has supported the U.S. and South Korea-led pressure campaign against Pyongyang since Kim Jong-un succeeded his father as DPRK leader in 2011. Yet, many if not most analysts believe that stability on the Korean Peninsula, rather than denuclearization, is the paramount priority of Chinese leaders with respect to the peninsula. Among other developments, the outbreak of war on the peninsula could lead to a massive flow of refugees into northeastern China, where large numbers of ethnic Koreans reside. For years, the United States and South Korea have sought to hold discussions with China about various contingencies involving military conflict with and/or instability in North Korea, in part to reduce the chances of a China-U.S./ROK military clash. Chinese officials generally have resisted engaging in these discussions. Some observers believe this might be in part to avoid appearing to countenance U.S./ROK military action to denuclearize the peninsula. Independent of such discussions, Chinese statements could complicate matters for the United States, as the possible articulation of Beijing's red lines could encourage the DPRK to continue taking aggressive action that falls just short of Chinese parameters for its rejection of Pyongyang's activities. The use of U.S. military force on the Korean Peninsula would likely have far-reaching implications for U.S. alliances and partnerships in the region, for great power politics and rivalries, and for the overall security landscape in the Asia-Pacific, and perhaps more broadly. An outbreak of war on the peninsula could potentially upend two U.S. overarching priorities in East Asia: preserving U.S. interests and maintaining stability in the region. This section examines some of the possible impacts for regional powers and U.S. interests in East Asia. Perhaps the most significant geopolitical question arising from a military conflict on the peninsula would be the effect on the U.S.-China relationship. Much would depend on China's involvement in the conflict, which could vary from hostile (challenging U.S./ROK forces in combat) to cooperative (working, for example, with the operation to secure the DPRK nuclear arsenal in the event of a regime collapse). During or after a military campaign, the Korean/Chinese border could become a geopolitically sensitive area, necessitating additional security forces. Regardless of the outcome, Washington and Beijing would likely be navigating new waters in the bilateral relationship. If Beijing remained officially "neutral," China may look to establishing its leadership in a changing East Asian order. It could decide to be more assertive in claiming maritime territory, particularly in the South China Sea, if U.S. forces were consumed in Northeast Asia. It might also seek to change the terms of its relationship, peaceably or by force, with Taiwan, either because U.S. attention and resources are deployed elsewhere, or as part of a deal with Washington for its cooperation on the Korean Peninsula. In such a case, U.S. commitments related to Taiwan's security would likely face existential questions, and the U.S.-China relationship would face a fundamental realignment. In postconflict reconstruction, China would likely play a major role, given its experience in building infrastructure, proximity to the area, and availability of foreign currency reserves to finance reconstruction. China's establishment in recent years of the Asian Infrastructure Investment Bank and its Belt and Road Initiative to boost economic connectivity within and across continents positions China well to perform such a role, and would heighten its influence. Even if the United States successfully executed a military campaign, China's capabilities would give Beijing considerable leverage in negotiations over the future of the peninsula, likely including discussions over whether a U.S. military presence would remain were the Korean Peninsula to be reunified. For U.S. bilateral alliances—most prominently with South Korea and Japan—U.S. willingness to use military force against North Korea could reinforce the credibility of U.S. commitment to its allies. The credibility of the U.S. mutual defense treaties could also be strengthened, although controversial issues such as the degree of consultation leading up to any strike could create fissures. If a military action were judged by Seoul and/or Tokyo to be Washington's choice alone—and particularly if the conflict resulted in mass casualties of their citizens—the alliances could be deeply shaken, or even abandoned. Despite years of preparation, the security partnerships could confront the inevitable challenges of operating in a wartime theater: (1) the strength of alliance planning, through decades of exercises and cooperation, would be tested; (2) issues such as operational control of the U.S./ROK forces would face immediate real-time challenges; (3) the logistical complexity of deploying troops and supplies to the theater from bases in Japan could encounter unanticipated obstacles; and (4) the ability of the Japanese Self Defense Forces to offer support for U.S./ROK military operations could pose difficult political questions for leaders in Seoul and Tokyo, given the distrust that seems to persist in Japan-South Korea relations. In the aftermath of a military operation, the alliances could face additional questions about U.S. commitment and obligation to its allies. If the use of U.S. military force successfully erases U.S. homeland vulnerability to a DPRK attack, allies might ask what responsibility the United States would have in assisting South Korea or Japan if military operations have damaged their countries (for more, see " Economic Impacts "). If the regime in Pyongyang falls, the process of reunification—even under the most optimistic conditions—faces daunting challenges given the stark differences between the two populations in terms of education, culture, societal organization, and familiarity with democratic or free market practices. The duration and extent of reconstruction efforts could also become a major area of contention. The two alliances could also face questions about their durability if the threat from North Korea is removed. The U.S.-ROK alliance in particular is based on defending the South from aggression from the DPRK; without the threat from North Korea, would Seoul feel the need to ally itself closely with the United States, or vice-versa, and would either party feel the need for a continued U.S. military presence? What other factors—especially pressure from Beijing—might sway Korean leaders? Russia's future role in the region is uncertain, even moreso in the event of a U.S. intervention. With Moscow thousands of miles away and with a relatively short border with the DPRK, Russia's security concerns are less immediate. However, Russia still maintains massive military capabilities that could be deployed to its Far East and complicate U.S./ROK operations. In addition, some maintain that the Kremlin has a strong interest in asserting itself in any emerging geopolitical order, and may seek to take advantage of a shake-up in the region. Some analysts argue that if the United States and its allies moved more aggressively to alter the situation on the Peninsula, or if the regime in Pyongyang collapsed on its own accord, Moscow and Beijing may find common cause in supporting North Korea. Both Russia and China share a strong desire to prevent a shift in the regional balance that a reunified peninsula under U.S. influence might produce. For illustrative purposes only, this section outlines potential options related to the possible use of military capabilities and their implications, along with attendant risks. Not all of these options are mutually exclusive, nor do they represent a complete list of possible options, implications, and risks. The following discussion is based entirely on open-source materials. CRS cannot verify whether any of these potential options are currently being considered by U.S. and ROK leaders. This list is intended to help elucidate the variety of ways that the military can be utilized in furtherance of foreign policy or national security objectives, and the different kinds of risks associated with different policy choices. As such, these notional options are intended to help Congress appreciate the different possible ways force might be employed to accomplish the goal of denuclearizing of the Korean Peninsula, or how the United States might respond to an initiation of hostilities by North Korea. The discussion of these options assumes no Chinese or Russian military intervention. Should either of those parties choose to become meaningfully involved, the strategic calculus would undoubtedly change in unpredictable and likely highly consequential ways. The design of a military campaign depends on the policy goals that leaders are seeking to accomplish. In August 2017, Secretary of State Tillerson and Secretary of Defense Mattis articulated the U.S. policy objective and parameters for the Korean Peninsula as the denuclearization of the Korean Peninsula.... [No] interest in regime change or accelerated reunification of Korea. We do not seek an excuse to garrison U.S. troops north of the Demilitarized Zone... [No] desire to inflict harm on the long-suffering North Korean people. If the U.S. objective is the denuclearization of the Korean Peninsula, U.S. and ROK leaders can seek to achieve this goal in a variety of ways. These range from increasing U.S. presence and posture on the Korean Peninsula, to communicating to Pyongyang—and possibly Beijing—that continuing along the current policy trajectory of nuclearization is counterproductive, or eliminating DPRK's nuclear and ICBM production capabilities and deployed systems, which would likely require intensive military manpower. The Trump Administration has not publicly detailed how it intends to advance toward the objective of denuclearization or, in particular, how the military might fit into such a campaign. From 2009 to 2016, Seoul and Washington tightly coordinated their respective North Korea policies, following a joint approach—often called "strategic patience"—that emphasized pressuring the regime to return to denuclearization talks through expanded multilateral and unilateral sanctions, attempting to persuade China to apply more pressure on Pyongyang, and boosting the capabilities of the U.S.-South Korea and U.S.-Japanese alliances. Despite the Trump Administration's casting of its "maximum pressure" approach as a departure from the Obama Administration's "strategic patience," numerous elements of their respective policies are similar: expanding U.S. and international sanctions, emphasizing China's ability to pressure North Korea, and coordinating policy with U.S. allies. Key changes from the Obama Administration's approach appear to be that the Trump Administration has raised the priority level of the North Korean threat, and Administration officials are openly discussing the possibility of a preventive military strike against North Korea. Maintenance of the military status quo would amount to a de facto continuation of the U.S. policy of inexorably increasing unilateral and multinational pressure through economic and diplomatic means to compel North Korea to change its behavior while simultaneously deterring DPRK aggression on the Korean Peninsula. Supporters of this course of action could argue that, of all the options available, it would be least likely to escalate the crisis on the Korean Peninsula for the immediate future, and that it provides time for international sanctions, which in their strictest forms began in 2016, to have an effect on North Korea. Other pressures, like increasing inflows of information perceived to be damaging to the regime into the DPRK, would also have more time to have an impact on the civilian population. Opponents of this course of action might argue that the policy of "strategic patience" failed to compel the DPRK to abandon its nuclear weapons and ICBM capabilities, and that North Korea is unlikely to abandon its WMD capabilities unless the Kim regime concludes that retaining them puts its survival at stake. Opponents might also argue that maintaining the status quo may create time for sanctions to work, but also creates time for North Korea to develop a nuclear-tipped ICBM capable of reaching the U.S. homeland and for North Korea to expand the size of that capability. In addition, some analysts are particularly concerned that South Korea and Japan may reassess their commitment not to build their own nuclear deterrent if North Korea is able to hold the United States at risk. Many analysts fear that Japan and South Korea "going nuclear" could set off a new arms race in Asia that would raise the risk of accidents or miscalculations in the region. This option is somewhat more robust than merely maintaining the status quo, with greater emphasis on using U.S. military presence and posture to deter and contain North Korea. Statements by the DPRK indicate that the U.S. presence on the Korean Peninsula has long been unpalatable to Pyongyang. Taking that into account, in addition to diplomatic and economic measures, U.S. leaders might seek to use the U.S. military presence to underscore the costs of DPRK nuclearization through enhancing its forward presence on the Korean Peninsula and in the region (on bases in Japan and Guam, for example). This could be done through prepositioning equipment, enhancing defensive capabilities, building up troop levels, and/or boosting trilateral cooperation among the United States, South Korea, and Japan. Underscoring the costs of DPRK nuclearization, such actions could also enhance deterrence of possible conflict while ensuring that critical systems and units are nearby in the event of hostilities. Recent dispatches of a U.S. carrier strike group and a Terminal High Altitude Area Defense (THAAD) missile defense deployment to South Korea are examples of this approach. The U.S. military has a wide array of prepositioned equipment, both at shore locations and afloat, that could be sent to South Korea or elsewhere within the region. Deploying additional ground troops to South Korea or elsewhere in the region is also an option. Redeploying U.S. tactical nuclear weapons onto the Korean Peninsula, as has been called for by the Liberty Korea Party, is another such option. Some observers further argue that a combination of enhanced missile defenses, cyber defenses, U.S./ROK military exercises, and monitoring and interdiction of shipments to prevent North Korean WMD proliferation will sufficiently contain the DPRK until peaceful denuclearization can occur. Skeptics could argue that such moves could be construed by Pyongyang as a prelude to a ground attack on the DPRK. They could also argue that U.S. presence might have little impact on the decisionmaking calculus of the Kim regime, since the current U.S. posture and rhetorical threats of the use of military force previously in the region have failed to dissuade the DPRK from acquiring nuclear capabilities and delivery systems thus far. In addition, there are political and diplomatic challenges to increasing military presence in places like Okinawa or achieving more effective trilateral U.S.-ROK-Japan security cooperation. Pursuing this option may mean deemphasizing, at least for the immediate future, the denuclearization of the Korean Peninsula and instead focusing on mitigating, or even negating, the means of delivery of nuclear devices, in particular nuclear-tipped ICBMs. Without sufficient testing, however, an ICBM's reliability and effectiveness could remain unknown. It may therefore be more difficult to threaten the U.S. homeland credibly with such a capability in the absence of further test launches, which North Korea is likely to pursue in the near term. The United States could attempt to shoot down every medium- and long-range missile and space launch with its ballistic missile defense (BMD) capabilities, such as the Aegis BMD, which is designed to intercept theater-range ballistic missiles, but not ICBMs. Supporters could argue that a course of action along these lines has several advantages, including the possible disruption of DPRK acquisition of a reliable nuclear ICBM without sending additional forces into the region, which, as discussed above, might arguably be seen as provocative by DPRK and other actors. It could also minimize risk to U.S. troops and their families in the region. Further, all North Korean missile tests are specifically prohibited by U.N. Security Council resolutions, which some proponents use as justification for such a course of action. Skeptics could argue that keeping one or more Aegis BMD ships in a relatively small geographic area for weeks or months on end could prevent the ships from performing other missions. In addition, two Aegis BMD ships in the 7 th Fleet continue to be out of service for months or longer. A major risk is the possibility that an intercept of a DPRK ballistic missile test launch might fail, thereby undermining that deterrent capability in an evolving crisis, with implications perhaps extending beyond the region. Finally, there are risks involved with shooting down a missile that could spread debris over land, air, or ocean areas that have not been cleared through various advance aviation and maritime warnings. Skeptics could also argue that the Kim regime could still respond militarily, which could escalate the conflict. North Korea would also still possess its nuclear weapons and could therefore proliferate either its nuclear material or weapons to other countries. Such a strategy also would not preclude Pyongyang from continuing to hold U.S. forces and installations—as well as U.S. allies including the ROK and Japan—at risk.  This course of action would mean focusing less on North Korea's voluntary denuclearization and more on eliminating, possibly through limited air strikes, DPRK's long-range ballistic missiles and associated facilities. Although the majority of the DPRK's missiles have been launched from fixed sites, efforts are reportedly underway in North Korea to develop solid-fuel mobile missiles that can be deployed more rapidly than liquid-fueled missiles before their launch and are harder to detect than missiles fired from known fixed sites. Reportedly, many DPRK ballistic missile development and production facilities are located in hardened sites in North Korea's northeastern mountainous regions near the Chinese border, adding an additional element of risk of Chinese intervention if these facilities are attacked. The DPRK is also believed to operate a single Sinpo-class diesel-electric submarine that may be able to launch a submarine-launched ballistic missile (SLBM); this submarine was used to test the DPRK's KN-11 SLBM. Diesel-electric submarines can be difficult to detect and therefore challenging to target in the event of a limited strike, especially if they are submerged and not moving much, perhaps even for U.S. anti-submarine warfare (ASW) capabilities. Under this option the United States could attack DPRK nuclear and ICBM facilities through airstrikes and cruise missile attacks. It is also possible that U.S. and ROK Special Operations forces could conduct direct action missions on the ground. These operations are considered to be high-risk—and could incur significant military casualties—compared with attacking targets with aerial assets. Advantages to this course of action may include the disruption of critical components of the DPRK's ICBM infrastructure, while signaling to Pyongyang that continuing its nuclear program is unacceptable, which could possibly bring the Kim regime back to the negotiating table. Skeptics could argue that this course of action might escalate, rather than deescalate, the conflict. Further, they could maintain that it might degrade, but not eliminate, North Korea's ICBM capabilities, perpetuating the crisis and possibly spurring the DPRK to pursue its ICBM and nuclear weapons capabilities even more aggressively and in a manner less conducive to such disruption. This option would be a more expansive military effort than the previous option, as it would involve targeting a greater number of facilities. Possible targets in a limited strike scenario include nuclear production infrastructure, nuclear devices and missile warheads, and associated delivery vehicles. Production infrastructure includes reactor complexes, uranium mines and enrichment facilities, plutonium extraction facilities, related research and development facilities, and explosive test facilities. Similar to the previous option, these targets could be attacked by air assets and cruise missiles. Ground attacks by SOF might also be an option. Proponents might argue that this option is most likely to eliminate the DPRK's nuclear program to the greatest extent without undertaking regime change. Skeptics, however, could argue that a distinct possibility exists that the DPRK would escalate the conflict rather than return to denuclearization negotiations. Given limited intelligence and extensive use of hardened underground facilities by North Korea, some experts believe U.S. strikes would not fully eliminate the country's nuclear weapons program, and "at best, they'll set the program back several years." They could also argue that striking nuclear device/weapon sites or facilities could result in widespread radioactive contamination in the event they are damaged or destroyed. Further, if North Korea's nuclear weapons program cannot be destroyed by U.S. strikes, any residual capability including significant conventional military forces—even if nuclear-capable missiles, submarines, or aircraft are eliminated—could be employed against South Korean and U.S. military and civilian targets, or other allied forces. Skeptics could also argue that there appears to be little information about the numbers, types, and whereabouts of DPRK nuclear devices and missile warheads, and that many of these facilities are believed to be underground in hardened facilities. Accordingly, finding and then eliminating these facilities would likely require highly manpower-intensive operations, and might therefore put considerable numbers of U.S./ROK forces at risk, possibly resulting in significant casualties. Although the Tillerson/Mattis op-ed specifically states that the United States has no interest in regime change on the Korean Peninsula, it remains a potential (if unlikely) option, particularly should the Kim regime behave in an aggressive manner toward the United States or its allies. A more comprehensive operation that might make regime survival untenable could involve strikes against not only nuclear infrastructure but command and control facilities, key leaders, artillery and missile units, chemical and biological weapons facilities, airfields, ports, and other targets deemed critical to regime survival. This operation would be tantamount to pursuing full-scale war on the Korean Peninsula, and risk conflict elsewhere in the region. Advocates of this argument might maintain that the root of the security challenge on the Korean peninsula is the Kim Jong-un regime itself, and that its elimination has the highest degree of likelihood of promoting regional and global security. Skeptics, however, could argue that eliminating the Kim regime involves a high degree of military and political risk, and that preparations for such a large-scale operation could be easily detected, possibly resulting in preemptive strikes by the DPRK against military and civilian targets. If an attack is suspected, they could argue, the DPRK could begin to disperse and hide units, making them more difficult to attack. Such a large-scale attack, opponents of pursuing regime change may say, could result in an escalation to a full-scale war if North Korea believes the operation is intended to decapitate the regime. A regime change operation, they could also argue, would likely require significant ground force involvement and would require a build-up of U.S. forces before it could be undertaken. In addition to possible participation in ground combat, they could argue, U.S. ground forces could be required for postconflict stabilization operations that could last years. With ongoing U.S. troop commitments in Iraq, Syria, and Afghanistan, such a substantial long-term presence on the Korean Peninsula could have significant ramifications for the availability and readiness of U.S. ground forces or, over the long term, for the required size of the U.S. military. Some observers contend that the only reason the DPRK views the United States as a risk is because U.S. troops are stationed in South Korea and Japan. One analyst states No one should expect a kinder, gentler Kim to emerge. But his "byungjin" policy of pursuing both nuclear weapons and economic growth faces a severe challenge, especially since sanctions continue to limit the DPRK's development. With the United States far away he would have more reason to listen to China, which long has advised more reforms and fewer nukes. He also might be more amenable to negotiate limits on his missile and nuclear activities, if not give up the capabilities entirely. Since nothing else has worked, an American withdrawal would be a useful change in strategy. Adherents to this view could maintain that withdrawing U.S. troops in exchange for DPRK denuclearization might eliminate or greatly alleviate any possibility of North Korean military action against the United States, and might even create greater latitude for internal political reform. Withdrawing U.S. Armed Forces from the Korean Peninsula, however, would not necessarily be accompanied by major changes in, let alone the termination of, the U.S.-ROK alliance; U.S. forces positioned elsewhere in the Asia-Pacific might be able to reinforce South Korea in the event of a crisis. Skeptics of this option could argue that given the history of North Korea not fully complying with agreements related to its nuclear capabilities, it is by no means certain that Pyongyang would follow through on such a deal over the long term. This could leave the United States in a worse position relative to a nuclear DPRK than it maintains at present. If not accompanied by a total verifiable dismantling and disposal of its nuclear and ballistic missile programs, North Korea could continue to threaten or coerce other countries in the region, and could continue its illicit materials trade with rogue states or nonstate actors. Furthermore, any degradation of the U.S. security relationship with South Korea—and a possible perceived abandonment of that long-standing ally—could erode the importance of military presence as a U.S. foreign policy tool elsewhere. The absence of a U.S. presence in South Korea might also encourage the DPRK to renew hostilities in order to unify the Korean Peninsula, a long-stated objective of successive Kim regimes, particularly as such a repositioning of U.S. Armed Forces, however, could make later reinforcement difficult to execute. In the event that the United States is believed to be either unreliable, not present, or both, South Korea—and possibly Japan—might deem it necessary to develop their own nuclear weapons. The situation on the Korean peninsula may prompt Congress to assess its role in any decisions regarding whether to commit U.S. forces to potential hostilities. The U.S. Constitution divides authority between Congress and the President on matters of war and the use of military force, and Congress may use its war powers to authorize, circumscribe, and in some situations prohibit U.S. forces from participating in hostilities. In assessing whether to exercise authority in this context, Congress might consider, among other things, the following: Does the President require prior authorization from Congress before initiating hostilities on the Korean Peninsula? If so, what actions, under what circumstances, ought to be covered by such an authorization? The Kim regime may continue to take aggressive action short of directly threatening the United States and its territories while it continues its path to acquire a nuclear ICBM capable of striking the United States. What might be the international legal ramifications for undertaking a preventive or preemptive strike without a U.N. Security Council mandate? How are these issues affected, if at all, by the fact that the Korean War was conducted under U.N. authority and that the armistice suspended hostilities but did not formally end the state of war between the DPRK and United Nations forces, which included U.S. forces? If the executive branch were to initiate and then sustain hostilities against North Korea—a nuclear-armed country—without congressional authorization, what are the implications for the preservation of Congress's role, relative to that of the executive branch, in the war powers function? How, in turn, might the disposition of the war powers issue in connection with the situation with North Korea affect the broader question of Congress's status as an equal branch of government, including the preservation and use of other congressional powers and prerogatives? Does the President require prior authorization from Congress before initiating hostilities on the Korean Peninsula? If so, what actions, under what circumstances, ought to be covered by such an authorization? The Kim regime may continue to take aggressive action short of directly threatening the United States and its territories while it continues its path to acquire a nuclear ICBM capable of reaching the United States. What might be the international legal ramifications for undertaking a preventive or preemptive strike without a U.N. Security Council mandate? Without a more detailed articulation of how the military might be employed to accomplish U.S. objectives on the Korean Peninsula, and a reasonable level of confidence about how the conflict might proceed, it is difficult to assess with any precision the likely fiscal costs of a military campaign, or even just heightened presence. Still, with the possible exception of full withdrawal, any other course of action listed in this report is likely to inc ur significant additional costs. Factors that might influence the level of expenditure required to conduct operations include, but are not limited to, the following: T he number of additional forces, and associated equipment, deployed to the Korean Peninsula or the Asia-Pacific theater more broadly. In particular, deploying forces and equipment from the continental United States (if required) would likely add to the costs of such an operation due to the logistical requirements of moving troops and materiel across the Pacific. T he mission set that U.S. fo rces are required to prosecute and its associated intensity . For example, those options leading to an increase of the U.S. posture on or around the Korean Peninsula for deterrence or containment purposes might require upgrading existing facilities or new construction of facilities and installations. By contrast, those options that require the prosecution of combat operations would likely result in significant supplemental and/or overseas contingency operations requests, particularly if U.S. forces are involved in WMD eradication or cleanup missions, or postconflict stabilization operations. The time required to accomplish U.S. objectives . As demonstrated by operations in Iraq and Afghanistan, the period of anticipated involvement in a contingency is a critical basis for any cost analysis. On one hand, a large stabilizing or occupying ground force to perform stabilization and reconstruction operations, for example, would likely require the expenditure of significant U.S. resources. On the other hand, a limited strike that does not result in conflict escalation would likely be relatively less expensive to the United States. The aftermath of a full-scale war on the Korean Peninsula could generate significant manpower requirements for U.S. forces. Department of Defense Instruction (DODI) 3000.0 Stability Operations specifies that the U.S. military has a critical role to play in "maintaining or reestablishing a safe and secure environment, providing essential government services, emergency infrastructure reconstruction, and humanitarian relief." U.S. forces have also provided logistical and communications support to affected governments in the wake of past humanitarian crises, such as the 2005 Pakistan earthquake and the 2004 Asian tsunami. Applied to a postconflict situation on the Korean Peninsula, the United States military might have to respond to a number of issues in both North and South Korea. North of the Demilitarized Zone, as many as 25 million North Koreans could be affected by a conflict, which could reduce already-scarce food and other essential supplies available to the general public. Further, approximately 80,000 to 120,000 prisoners in prison camps could be released and may need immediate attention. South of the DMZ, the Republic of Korea could need significant assistance recovering and reconstructing key infrastructure, such as fuel and electricity services, contending with casualties, delivering emergency supplies, and much more. Depending on the circumstances, U.S. forces might be asked to assist their ROK counterparts in disarming and demobilizing North Korea's military. Some analysts suggest that the ROK might also have to prepare for and counter sabotage and attempts to foment insurgency by any remaining North Korean SOF. Should the DPRK target other U.S. allies in the region, or U.S. installations in Japan or Guam, U.S. forces could be required to assist with postconflict reconstruction in those locations as well. An additional factor that could affect both sides of the DMZ would be the use of weapons of mass destruction, including chemical, biological, and nuclear weapons. Beyond the costs involved, decontaminating affected areas would likely require significant manpower and medical support. Given the possible spread of WMD contamination in the atmosphere, assistance with cleanup might be required in other countries as well. In addition to performing cleanup operations, which could require significant manpower, U.S. personnel might be directed to help locate and eliminate DPRK WMD stockpiles north of the DMZ. Another factor affecting the possible costs of operations—before, during, and after a conflict—is the willingness and availability of other states, such as Japan or even China, to contribute financial or military resources toward prosecuting a war and stabilizing the Korean Peninsula. Such contributions could bring international legitimacy to U.S./ROK military efforts, especially if some states in the international community advance the view that any U.S. action, intended or inadvertent, was preventive rather than preemptive in nature. Another dynamic worth considering is the role of Beijing in postconflict stabilization and/or eradicating DPRK weapons of mass destruction programs. Such activities, as mentioned earlier, would likely require significant troop deployments north of the DMZ. Assuming China chooses not to become involved militarily in a conflict on the peninsula, and given that China has indicated its strong preference to maintain a buffer state and existing political structures in North Korea, China may consider deploying forces across its border to stabilize the DPRK. Alternatively, China may also consider assisting U.S. military operations. However, it is not known whether China possesses the capability to eliminate WMD facilities, particularly those that might be underground. These factors, and others, would likely face Congress should the President submit a request for additional monies to support increased military activity on or around the Korean Peninsula. With that in mind, Congress could consider the following: The potential costs of heightened U.S. operations on the Korean Peninsula, particularly if they lead to full-scale war and significant postconflict operations. The need for the United States to reconstitute its forces and capabilities, particularly in the aftermath of a catastrophic conflict. The impact of the costs of war and postconflict reconstruction on U.S. deficits and government spending. The costs of a conflict on the Korean Peninsula to the global economy. The extent to which regional allies, and the international community more broadly, might contribute forces or resources to a military campaign or its aftermath. Particularly should hostilities escalate into a full-scale war between the DPRK and the U.S./ROK, the force for conducting such a military campaign and then managing its aftermath could be considerable. Given ongoing U.S. military commitments elsewhere, conducting these conflict and postconflict operations could cause significant strain on U.S. forces. It might be difficult to redirect forces from the Korean theater to other contingencies such as Iraq, Syria, Eastern Europe, or elsewhere, should they arise. Other key inventories, such as missile defenses, might need to be regenerated. Separate but related is the matter of multiple efforts that would need to be conducted and resourced simultaneously on the Korean Peninsula alone. For example, noncombatant evacuation operations—for upwards of 500,000 U.S. citizens—might need to be conducted alongside logistic operations to flow additional forces into theater. Should these two competing requirements result in a higher demand for naval and other capabilities than supply permits, difficult tradeoffs in terms of global force management might need to be made. Congress might consider, among others, the following questions: What might be the order of priority for U.S. operations in the event of a conflict? What might be the priority of combat operations relative to other critical missions that might tax U.S. military capabilities, such as noncombatant evacuation operations? What, if any, impact has the Budget Control Act had on the readiness of U.S. forces to engage in hostilities on the Korean Peninsula? How might force requirements for a Korean scenario be balanced against those for other pressing national security concerns in other theaters? Does DOD have sufficient force structure to adequately fulfill responsibilities elsewhere while conducting expanded operations in Korea? Is the Department of Defense making appropriate planning and force structure decisions to be able to respond to multiple contingencies if necessary? Does DOD need to adjust its force planning construct? Few analysts believe that North Korea would launch an unprovoked attack on U.S. territory. Nonetheless, as the crisis on the Korean peninsula continues to evolve, Congress could confront significant questions regarding its role in shaping U.S. policy in the region. Ultimately, Congress may have face two determinations. First, whether or not it believes the United States could or should manage and deter a nuclear-armed North Korea if it becomes capable of attacking the U.S. homeland. Second, whether taking decisive action to prevent the emergence of such a DPRK capability, including the use of military forces, might be necessary. Such determinations potentially carry considerable risks for the United States, its allies, regional stability, and global order. Particularly given emerging questions about the U.S. role in the world, how the United States chooses to contend with the DPRK nuclear weapons and ICBM programs also raises broader strategic questions with which Congress may grapple: How would any particular course of action impact U.S. interests, both regionally and globally? How would allies and partners perceive U.S. efforts to accomplish denuclearization, and would that affect their willingness to accept the United States as a global leader? What might be the economic, international political, and strategic effects of an erosion of U.S. standing in the global order, if any? What impacts would U.S. action regarding North Korea have on alliances around the world, such as those the United States maintains with Australia and NATO? What effects would the outbreak of war on the Korean peninsula have upon the U.S. economy? What implications would U.S. Korean policy choices have for existing nuclear, chemical, and biological weapons nonproliferation regimes? Appendix A. In Detail: The Military Balance on the Korean Peninsula Estimating the military balance in the region, and how military forces might be employed during wartime, requires accounting for numerous variables and as such is an inherently imprecise endeavor. As an overall strategic approach, the DPRK has emphasized quantity over quality, as well as asymmetric capabilities including weapons of mass destruction and special operations forces, in building and maintaining its military. The Republic of Korea, by contrast, has emphasized quality over quantity, and maintains a highly skilled, well-trained, and capable conventional force. Not counted in this assessment are the capabilities of China, Russia, or other regional U.S. allies (such as Japan or Australia) who could play a role in a conflict on the Korean Peninsula or its aftermath. An Overview of DPRK Military Capabilities Although the Korean People's Army (KPA)—a large, ground force-centric organization comprising ground, air, naval, missile, and SOF—has over 1 million soldiers in its ranks, making it the fourth-largest military in the world, it has some significant deficiencies, particularly with respect to training and aging (if not archaic) equipment. A number of analysts attribute that degradation of capability to food and fuel shortages, economic hardship, and an inability to replace aging equipment, among other factors. As such, particularly in recent years, the KPA appears to have invested heavily in asymmetric capabilities, both on the high and low end of the capability spectrum. These high and low capabilities are in addition to the considerable DPRK inventory of long-range rockets, artillery, short-range ballistic missiles, and chemical weaponry aimed at targets in the Republic of Korea. U.S. military facilities and the Seoul region, with a population of approximately 23 million, are within range of DPRK conventional artillery situated along the border. Reports indicate that the DPRK has made mobile its missile launchers and at least some of its artillery batteries, arguably making them more difficult to target. Further, reports suggest the DPRK has hardened many of its key facilities through an extensive network of underground tunnels, a further challenge to fully understanding the DPRK's military capabilities. Conventional Forces Of North Korea's 24 million people, 4% to 5% serve on active duty, and another 25% to 30% are assigned to a reserve or paramilitary unit and would be subject to wartime mobilization. Conscripts are required to serve for 10 years. With approximately 70% of its ground forces and 50% of its air and naval forces deployed within 100 kilometers of the DMZ, the KPA poses a continuous threat to the ROK and U.S. forces stationed there. The KPA primarily fields legacy equipment, either produced in or based on designs from the Soviet Union and China dating back to the 1950s, 1960s, and 1970s. Although a few of its weapons systems are based on modern technology, the KPA in general has not kept pace with regional military capability developments. The KPA has not acquired new fighter aircraft in decades, relies on older air defense systems, and lacks ballistic missile defense. Its Navy does not train for blue water operations, but the KPA does conduct regular military exercises. Analysts question whether its conventional force training scenarios are sufficiently realistic, especially since the KPA has not been combat tested in over six decades. Taken together, some question whether the conventional component of the KPA would be able to translate its quantitative supremacy into meaningful military advantage. Component-Specific Capabilities Ground. The KPA's ground forces are predominantly regular and light-infantry units, supported by armor and mechanized units and heavy concentrations of artillery. These forces are forward-deployed, fortified in several thousand underground facilities, and include long-range cannon and rocket artillery forces capable of reaching targets in Seoul from their garrisons. The ground forces possess numerous light and medium tanks, and many armored personnel carriers. The KPA's large artillery force includes long-range 170 mm guns and 240 mm multiple rocket launchers (MRL), many deployed along the DMZ, posing a constant threat to northern parts of the ROK. In recent years, North Korea has unveiled other new ground force equipment, including tanks, artillery, armored vehicles, and infantry weapons. Air and Air Defense. The North Korean Air Force (NKAF), a fleet of more than 1,300 aircraft—mostly legacy Soviet models—is primarily responsible for defending North Korean air space. Its other missions include SOF insertion, transportation and logistics support, reconnaissance, and tactical air support for KPA ground forces. However, because of the technological inferiority of most of its aircraft fleet and rigid air defense command and control structure, much of North Korea's air defense is provided by surface-to-air missiles (SAMs) and anti-aircraft artillery (AAA). The NKAF's most capable combat aircraft are its MiG-29 FULCRUMs, procured from the Soviet Union in the late 1980s; its MiG-23 FLOGGERs; and its SU-25 ground-attack FROGFOOT aircraft. However, the majority of its aircraft are less capable MiG-15s, MiG-17s, MiG-19s (F-6s), and MiG-21s. The NKAF operates a large fleet of An-2 COLT aircraft, which are 1940s vintage single-engine, 10-passenger biplanes, likely tasked with inserting SOF into the ROK. The Air Force is rounded out with several hundred helicopters, which would be used for troop transport and ground attack, including predominantly Mi-2/HOPLITE and some U.S.-made MD-500 helicopters obtained by circumventing U.S. export controls in 1985. North Korea possesses a dense, overlapping air defense system of SA-2, SA-3, and SA-5 SAM sites, mobile SA-13 SAMs, mobile and fixed AAA, and numerous man-portable air-defense systems like the SA-7. As the NKAF's aircraft continue to age, it increasingly relies on its ground-based air defenses and on hiding or hardening assets to counter air attacks. To help make up for these deficiencies in its air forces, the DPRK has acquired drones that are thought to be capable of delivering chemical and biological payloads, as well as performing reconnaissance missions. Naval . The North Korean Navy (NKN) is the smallest of the KPA's three main services. This coastal force is composed primarily of numerous, though aging, small patrol craft that carry a variety of anti-ship cruise missiles, torpedoes, and guns. The NKN maintains one of the world's numerically largest submarine forces, with around 70 attack-, coastal-, and midget-type submarines. In addition, the NKN operates a large fleet of air-cushioned hovercraft and conventional landing craft to support amphibious operations and SOF insertion. The force is divided into East and West Coast Fleets, which each operate a variety of patrol craft, guided-missile patrol boats, submarines, and landing craft. North Korean Nuclear Capabilities North Korea has recently made considerable strides toward acquiring strategic nuclear capabilities. North Korea has tested six nuclear devices—one in 2006, one in 2009, one in 2013, two in 2016, and one in 2017—and has declared itself to be a nuclear-armed state. Since the Six-Party nuclear talks broke down in 2009, North Korea has restarted its plutonium-production reactor and has openly built a uranium enrichment plant (and may have clandestine enrichment facilities). Some nongovernmental experts estimate that North Korea could have potentially produced enough material for 13-21 nuclear weapons, and could now produce enough nuclear material for an additional seven warheads per year. A Washington Post report from August 2017 quotes one component of the intelligence community, the U.S. Defense Intelligence Agency (DIA), as assessing that North Korea had achieved this step. The same report said the DIA had asserted that North Korea may have a stockpile of up to 60 nuclear warheads, much higher than most open-source estimates. North Korea has also threatened to use its nuclear weapons in an electromagnetic pulse (EMP) attack, which involves detonating a nuclear warhead above the earth's atmosphere, potentially disrupting and damaging critical infrastructure. Ballistic Missile Technology Over the past 20 years, North Korea attempted six satellite launches using long-range ballistic missile technology. There is reported evidence that each held a small satellite payload. The first four launches failed, but the latest two (in 2012 and 2016) placed satellites in orbit. The U.S. intelligence community has assessed that DPRK space launch capabilities share many of the same technologies that could be used in an ICBM program. In addition, Pyongyang tested both medium-range (estimated 3,000-kilometer range) "Musudan" missiles and a submarine-launched ballistic missile in 2016. Improvements in medium-range missiles suggest that North Korea could credibly threaten large U.S. bases and population centers in Japan and South Korea. See Figure 2 and Appendix C for the population centers and military bases that could be within range of these missiles in Korea, Japan, and Guam. In July 2017, North Korea test-launched two long-range ballistic missiles that some observers characterized as having intercontinental range, achieving a capability milestone years earlier than predicted. The liquid-fueled missiles flew in a lofted or very high trajectory, demonstrating a theoretical range that could include Hawaii, Alaska, Guam, or even the continental United States. Figure A-4 illustrates the areas within potential reach of these missile tests had they not been lofted, according to a range of observers. It is not known what payload was used, but the actual range of those missiles using a nuclear warhead would likely be significantly shorter (because of the weight of an actual warhead). Regardless, almost all observers agree that North Korea appears intent on deploying an operational nuclear ICBM capability. Few analysts believe that North Korea would launch an unprovoked attack on U.S. territory. Some, such as Russia, argue that this test was more accurately a medium-range ballistic missile with potential range of 3,500-5,500 km. Other technical experts have pointed out a fairly clear Soviet/Russian technology heritage in the major missile components used in these tests, as well as smaller components that observers believe were acquired illicitly through a range of Chinese entities. Such cooperation among these countries on ballistic missile development goes back decades. Unconventional Warfare Capabilities Pyongyang has also invested in its special operations forces, which some believe could be employed against U.S./ROK targets—particularly to conduct sabotage, launch terrorist attacks, and wage unconventional warfare—in the event of an outbreak of hostilities on the Korean Peninsula. North Korean SOF are considered among the most highly trained, well-equipped, best-fed, and highly motivated forces in the KPA. As North Korea's conventional capabilities decline relative to the ROK and United States, North Korea appears increasingly to regard SOF capabilities as essential for asymmetric coercion. Estimates vary on the size of DPRK SOF, although U.S. and ROK intelligence and military sources maintain that its end strength may be as high as 200,000, including 140,000 light infantry and 60,000 in the 11 th Storm Corps. The latter is primarily focused on training and undertaking special and unconventional warfare. According to the Department of Defense SOF units dispersed across North Korea appear designed for rapid offensive operations, internal defense against foreign attacks, or limited attacks against vulnerable targets in the ROK as part of a coercive diplomacy effort. They operate in specialized units, including reconnaissance, airborne and seaborne insertion, commandos, and other specialties. All emphasize speed of movement and surprise attack to accomplish their missions. SOF may be airlifted by AN-2 COLT aircraft or helicopters (and possibly Civil Air Administration transports), moved by maritime insertion platforms, or travel on foot over land or via suspected underground, cross-DMZ tunnels to attack high-value targets like command and control nodes or air bases in the ROK. Some also believe that SOF sleeper agents have been planted in South Korea. Cyber Capabilities Among governments that pose cyber threats to the United States, some analysts consider the North Korean threat to be exceeded only by those posed by China, Russia, and Iran. North Korea appears to be engaging in increasingly hostile cyber activities, including theft, website vandalism, and denial of service attacks. Whether North Korea has the capability to go beyond mere nuisance to more destructive cyberattacks on critical infrastructure is a matter of debate. Some reports suggest that North Korea has a sophisticated and burgeoning offensive cyber capability. Others assess North Korea as lacking the infrastructure and native technical skill necessary to undertake destructive cyberattacks. Still others note that some of the attacks ascribed to North Korea appear relatively unsophisticated and enabled by the targets' poor network security. In 2014, General Curtis M. Scaparrotti, then-Commander, United Nations Command and the Republic of Korea Combined Forces, offered the following assessment: North Korea employs computer hackers capable of conducting open-source intelligence collection, cyber-espionage, and disruptive cyber-attacks. Several attacks on South Korea's banking institutions over the past few years have been attributed to North Korea. Cyber warfare is an important asymmetric dimension of conflict that North Korea will probably continue to emphasize—in part because of its deniability and low relative costs. Relying on Korean and English resources, the Center for Strategic and International Studies concluded in a 2015 report: Left unchecked and barring any unpredictable power shift, North Korea is likely to continue to place strategic value in its cyber capabilities. Future North Korean cyberattacks are likely to fall along a spectrum, with one end being continued low intensity attacks and the other end characterized by high intensity attacks from an emboldened North Korea. Concurrently, the DPRK will likely deepen the integration of its cyber elements into its conventional military forces. Some observers suggest that, because there is little visibility into North Korea's activities, the possible threats from North Korean cyber activities are often inflated. An assessment released by the Korea Economic Institute found that the international community's "fears of the unknown increase the risk of threat inflation dramatically." These analysts contend that although North Korea may have the capability to undertake global cyber nuisance or theft-motivated activities, the nation lacks the ability to undertake operations that are "complex or as devastating as the Stuxnet attack, a computer virus that disrupted Iran's nuclear program." In November 2014, Sony Pictures Entertainment experienced a cyberattack that disabled its information technology systems, destroyed data, and accessed internal emails and other documents that were then leaked to the public. Hackers then sent emails, threatening "9/11-style" terrorist attacks on theaters scheduled to show the film The Interview . The Federal Bureau of Investigation (FBI) publicly attributed the 2014 hacking of Sony Pictures Entertainment to the North Korean government. Starting in 2009, North Korea is alleged to have conducted multiple cyberattacks on South Korean financial institutions and media outlets. The Department of Homeland Security issued a bulletin in June 2017 suggesting that North Korea is targeting the media, aerospace, financial, and critical infrastructure sectors in the United States. An Overview of ROK Military Capabilities The Republic of Korea has steadily improved its conventional forces, increasing their lethality through improvements in command, control and communications, advanced technology, and by incorporating lessons from its experience in Operation Iraqi Freedom. Still, the size of the ROK active duty military is approximately half that of the DPRK's, leading some analysts to conclude that South Korea may not be able to mass enough force to meet its needs. To date the ROK has decided not to acquire its own nuclear weapons, due to its reliance on U.S. security assurances, including in particular the American extended deterrent nuclear umbrella. There have been recent calls to redeploy U.S. tactical nuclear weapons to South Korea. Component-Specific Capabilities Ground Forces . The ROK Army (ROKA) has primary responsibility for defending the Republic of Korea, and it has an end strength of approximately 490,000, and an active reserve force of 600,000. ROKA consists of the Army Headquarters; two Field Army Commands, tasked with defense of their respective areas of responsibility, which includes terrain up to the South Korean border of the Demilitarized Zone; the Second Operations Command, with the role of maintaining rear-area stability and war-sustaining capabilities; the Capital Defense Command, which is responsible for the protection of key facilities and infrastructure in Seoul; and other commands, which are responsible for Special Operations, aviation operations, personnel and logistics support, and education and training. Naval Forces . The ROK Navy, which is organized under the Navy headquarters, has an approximate end strength of 70,000, including 29,000 in its Marine Corps. It comprises the Naval Operations Command, which has command authority over naval operations overall, including anti-surface operations, anti-submarine operations, mine and counter-mine operations, and amphibious operations. The ROK's three Fleet Commands, which are subordinate to the Naval Operations Command, conduct defensive missions by deploying surface combatants such as destroyers, frigates, patrol vessels, and patrol craft. Submarine Force Command, also subordinate to Naval Operations Command, carries out operations involving submarine use. ROK's Marine Corps Headquarters, which operates ROK's Quick Task Forces and Quick Reaction Forces, is in charge of amphibious operations and has a mission set that includes defense operations in assigned areas, including coastal islands. Finally, the Northwest Islands Defense Command is responsible for the defense of the northwestern islands and provides logistics and training support to the Navy. Air Forces. Organized under the Headquarters, the ROK Air Force comprises approximately 65,000 personnel and has three primary commands: Operations Command, Logistics Command, and Evaluation and Training Command. Air Force Operations Command has command authority over all air operations, including counter-air, air interdiction, and close-air support operations, and has four subordinate commands: (1) Air Combat Command; (2) Air Mobility and Reconnaissance Command; (3) Air Defense Missile Command, which carries out air defense missions against airborne attacks by enemy aircraft and missile attacks; and (4) Air Defense Control Command, which is responsible for air control in the Korean Peninsula theater, air surveillance, aircraft identification, and air support. ROK Missile Defenses Since 2010, the United States has engaged its allies in the Asia-Pacific, specifically Japan, South Korea, and Australia, to develop and implement an integrated regional BMD capability to deter and counter North Korea ballistic missile threats. Over the past 15 years, the United States has learned how its own BMD capabilities are significantly enhanced by integrating them into a much larger global BMD System (BMDS). The U.S. contribution to NATO's territorial defense against possible ballistic missile threats from Iran, for example, has led to a phased capability to deploy THAAD radar, sea-based Aegis BMD, and Aegis Ashore capabilities in Europe, and to fully integrate those with the current and prospective range of NATO European BMD capabilities. The concerted effort to develop a similar capability in Northeast Asia has not been as successful, primarily because of outstanding historical and political issues between South Korea and Japan. The inability to fully integrate regional BMD systems among U.S., Korean, and Japanese BMD systems results in an unrealized potential that could prove significant if conflict erupts. Aegis Ballistic Missile Defense (BMD) . The South Korean Navy has three Aegis destroyers that are similar to U.S. Navy Arleigh Burke (DDG-51)-class Aegis destroyers. The ships, which entered service in 2008, 2010, and 2012, are known as the Sejon Daewang (KDX-3) class. Three additional KDX-3 ships are planned and may enter service in 2023-2027, according to the 2016-2017 edition of IHS Jane's Fighting Ships . The three additional ships, according to this source, may be built with a BMD-capable version of the Aegis system. The three existing ships are equipped with a version of the Aegis system that is not BMD capable. The Aegis system on the three existing ships can be modified to become BMD sensor-capable, and South Korea reportedly has plans to do this, but that modification is to be done in the future. The three existing Aegis destroyers have participated in U.S.-South Korean-Japanese military exercises. Given their current lack of BMD capability, their potential contribution to any near-term BMD mission would be an indirect one—they could help defend U.S. and Japanese BMD-capable ships from North Korean submarines, surface ships, aircraft, and anti-ship cruise missiles. Terminal High Altitude Air Defense (THAAD) . South Korea agreed to host a U.S. THAAD battery in 2016. That battery was deployed earlier this year in south central South Korea with four of the eight intended launchers. Until recently, the remaining four launchers had been held up due to outstanding political and environmental challenges. The operational status of the battery is classified, but observers believe the battery is already fully operational, with its eight launchers and its 48 interceptors. THAAD is widely considered to be highly effective against short-range ballistic missiles (SRBM) and medium-range ballistic missile (MRBM) threats based on its operational test performance over the past many years. THAAD has not been used in conflict, so its wartime performance is untested. THAAD is designed to protect larger areas, such as parts of South Korea including Camp Humphreys and other military assets, for example. It is unclear, however, whether THAAD could counter ballistic missiles targeted against Seoul, because that city lies just outside the unclassified operational effectiveness range from where this THAAD battery is located. Patriot . South Korea currently has a Patriot Advanced Capability-2 missile defense system at the Osan military base in Seoul. South Korea is in the process of receiving upgrades to Patriot Advanced Capability-3, which then-U.S. Army Secretary Eric Fanning said in 2016 would be completed by 2018. The Patriot PAC-2 has demonstrated limited wartime capability against SRBM threats, and while the PAC-3 system has performed well in operational tests according to DOD, it has not been used in conflict. South Korea has been developing an indigenous BMD capability against SRBMs called Korean Air and Missile Defense (KAMD). In 2016, Korea Defense Minister Han Min-Koo stated that the PAC-3 capability would be deployed in 2020 and 2022 as a part of the KAMD system. In April 2017, the Ministry of National Defense released the 2018-2022 Mid-Term National Defense Plan. This plan includes KAMD as part of a "three-axis system," which also includes a "kill chain" for a preemptive strike in response to signs of an imminent North Korean missile attack and a Korean Massive Punishment and Retaliation (KMPR) system for retaliating directly against the North Korean leadership in the event of a nuclear attack. As a part of efforts to move up development of these capabilities, the South Korean military is working to hasten performance improvements in its medium-range surface-to-air missile (M-SAM) system. These capabilities are currently not available in the near term. Cyber Capabilities The Republic of Korea is one of the world's most wired countries, making it potentially vulnerable to cyberattacks. In contrast, North Korea has one of the smallest Internet presences in the world and lacks the same widespread dependence on networked technologies. The Republic of Korea has been seeking to develop its own offensive cyber capabilities since 2014, moving from a doctrine of more defensive cyber measures. According to Yonhap News Agency, an anonymous military source stated that "[To date] the military had focused on monitoring-based operations to deter enemies' hacking attempts, but now we will proactively detect hosts of such attacks online and launch preemptive strikes to prevent them from victimizing us from the outset." The Defense Ministry also announced plans to bring its total cyber force to approximately 1,000 troops, operating under the South Korean Ministry of Defense's Cyber Command created in 2010. In 2016, it was reported that the South Korean Cyber Command was hacked by North Korea. In April 2015, then-U.S. Secretary of Defense Ashton Carter and Korean Defense Minister Han held a press conference in which they noted the achievements of close ROK-U.S. coordination on the cyberattacks on Sony, and the intent to reinforce this cooperation in response to North Korean and international cyber threats. U.S.-ROK cyber defense coordination predates the Sony attacks (discussed above). In 2014, a new facility for cybersecurity was created to allow U.S. Forces Korea to coordinate efforts with other U.S. commands as well as Republic of Korea civilian government and military forces. The U.S. Forces Korea Joint Cyber Center serves as the focal point for increasing international cooperation between U.S. and Korean forces in their defensive measures against increasing cyber aggression from North Korea. Also in 2014, Korean and U.S. forces held the first bilateral cyber tabletop exercise. U.S. Support to the Republic of Korea There are 28,500 U.S. troops and their families currently stationed in the Republic of Korea, primarily playing a deterrent role by acting as a tripwire in case of DPRK hostilities south of the DMZ. U.S. forces also train with their ROK partners to better prepare them to participate in coalition operations in other theaters. The United States reportedly also provides the ROK with several key enablers, including military intelligence. Since 2004, the U.S. Air Force has increased its presence in ROK through the regular rotation into South Korea of advanced strike aircraft. These rotations do not constitute a permanent presence, but the aircraft often remain in South Korea for weeks and sometimes months for training. Due to these conventional capabilities, as well as the U.S.-ROK Mutual Defense Treaty, the United States has extended its deterrent umbrella to South Korea, including nuclear deterrence. Under current U.S./ROK operational plans (OPLANS), the United States plans to deploy units to reinforce the ROK in the event of military hostilities. In the event of wartime and depending on those circumstances, up to 690,000 additional U.S. forces could be called upon to reinforce U.S./ROK positions, along with 160 naval vessels and 2,000 aircraft. These units and their estimated arrival date in theater are listed in the Time-Phased Force Deployment List (TPFDL). These units include both Active and Reserve Component units from all services and arrival dates can range from days to weeks or months, depending on (1) the operational need for the unit, (2) the readiness status of the unit, and (3) the availability of strategic air and sealift. Furthermore, according to reports, since 2015 the U.S. and ROK militaries have prepared and exercised new war plans to strike North Korean WMD facilities and top leadership in an emergency situation. 56 According to the Ministry of Defense of the Republic of Korea, augmentation forces are to be increased progressively based on how the crisis situation develops, in two different modes: namely, the Flexible Deterrence Options (FDO) and the Time Phased Force Deployment Data (TPFDD). The FDO are enacted during the initial stages of a conflict when the level of crisis rises in the Korean peninsula, to deter war and mitigate the crisis situation by deploying designated forces. If the attempt to deter war fails, combat and support forces, as pre-planned under the TPFDD, will be deployed to execute the ROK-US combined operations plan. Should activating the Reserve Component units become necessary, some form of mobilization would be required, involving Congress, the President, the Secretary of Defense, or military department Secretaries, depending on the specific mobilization category. Also, most Reserve Component units (as well as some Active units) could require additional personnel, equipment, and training before being certified ready for deployment, and these considerations are factored into the TPFDL as well. U.S. Posture on the Korean Peninsula The U.S. military is in the process of relocating its forces farther south from bases near the border with North Korea, with South Korea paying $9.7 billion for construction of new military facilities. The realignment plan reflects the shift toward a supporting role for U.S. Forces Korea (USFK) and a desire to resolve the issues arising from the location of the large U.S. Yongsan base in downtown Seoul. Some observers contend that another initial rationale for the move, which was discussed as early as 2003, was to remove U.S. forces from DPRK artillery range. Others, including the DPRK, contend that the consolidation of the U.S. footprint has actually made American forces more vulnerable, as larger massed locations are easier to target than smaller, dispersed installations. The USFK base relocation plan has two elements. The first involves transferring a large percentage of the 9,000 U.S. military personnel at the Yongsan base to U.S. Army Garrison (USAG) Humphreys, which is located near the city of Pyeongtaek some 40 miles south of Seoul. The second element involves relocating about 10,000 troops of the Second Infantry Division from the Demilitarized Zone to areas south of the Han River (which runs through Seoul). The end result would be that USFK sites decline to 96, from 174 in 2002. The bulk of U.S. forces are to be clustered in the two primary "hubs" of Osan Air Base/USAG Humphreys and USAG Daegu that contain five "enduring sites" (Osan Air Base, USAG Humphreys, USAG Daegu, Chinhae Naval Base, and Kunsan Air Base). U.S. counter-fires (counter-artillery) forces stationed near the DMZ are the exception to this overall relocation. The United States and South Korea agreed that those U.S. units would not relocate to USAG Humphreys until the South Korean counter-fires reinforcement plan is completed around 2020. 81 The city of Dongducheon, where those soldiers are based, has protested this decision and withdrawn some cooperation with the U.S. Army. 82 United States Pacific Command (USPACOM) USPACOM was established on January 1, 1947, and is the oldest of the United States' unified combatant commands. Its Area of Responsibility (AOR) consists of 36 nations and contains some of the world's busiest international sea lanes. USPACOM is commanded by Admiral Harry Harris, USN. USPACOM's headquarters is supported by a number of component and subunified commands, including U.S. Forces Korea, U.S. Forces Japan, U.S. Special Operations Command Pacific, U.S. Pacific Fleet, U.S. Marine Forces Pacific, U.S. Pacific Air Forces, and U.S. Army Pacific. Approximately 375,000 U.S. military and civilian personnel are assigned to USPACOM and its different components across the Indo-Asia-Pacific region. According to USPACOM, those assignments are broken out as follows: U.S. Pacific Fleet consists of approximately 200 ships (including five aircraft carrier strike groups), nearly 1,100 aircraft, and more than 130,000 sailors and civilians. Marine Corps Forces, Pacific includes two Marine Expeditionary Forces and about 86,000 personnel and 640 aircraft. U.S. Pacific Air Forces comprises approximately 46,000 airmen and civilians and more than 420 aircraft. U.S. Army Pacific has approximately 106,000 personnel from one corps and two divisions, plus over 300 aircraft assigned throughout the AOR. These component command personnel figures also include more than 1,200 Special Operations personnel. Department of Defense civilian employees in the Pacific Command AOR number about 38,000. Of note, approximately 28,500 U.S. servicemembers and their families are stationed in the Republic of Korea, while U.S. Forces Japan consists of approximately 54,000 military personnel and their dependents. As of September 2016, approximately 5,000 servicemembers and their families were stationed in Guam. Command and Control Established on November 7, 1978, the ROK/U.S. Combined Forces Command (CFC) is the warfighting headquarters. Its role is to deter, or defeat if necessary, outside aggression against the ROK. To accomplish that mission, the CFC has operational control over more than 600,000 active-duty military personnel of all services, of both countries. In wartime, augmentation could include some 3.5 million ROK reservists as well as additional U.S. forces deployed from outside the ROK. If North Korea attacked, the CFC would provide a coordinated defense through its Air, Ground, Naval, and Combined Marine Forces Component Commands and the Combined Unconventional Warfare Task Force. In-country and augmentation U.S. forces would be provided to the CFC for employment by the respective combat component. The CFC is commanded by a four-star U.S. general, with a four-star ROK Army general as deputy commander. The United States has agreed to turn over the wartime command of Korean troops to South Korea, but the two sides have postponed this transfer for several years. Under the current command arrangement, which is a legacy of U.S. leadership of the U.N. coalition in the 1950-1953 Korean War, South Korean soldiers would be under the command of U.S. forces if there were a war on the peninsula. The plan to transfer wartime operational control recognizes South Korea's advances in economic and military strength since the Korean War and is seen by many Koreans as important for South Korean sovereignty. Progressive parties in South Korea generally support hastening the transition, arguing that the U.S. presence influences North Korea to accelerate its military buildup. Under a 2007 agreement, the CFC, which has been headed by the U.S. commander in Korea, is to be replaced with separate U.S. and ROK military commands; the provisional name of the new U.S. command is Korea Command (KORCOM). When the U.S. and ROK militaries operate as a combined force under the new command structure, U.S. forces may be under the operational command of a Korean general officer, but U.S. general officers are to be in charge of U.S. subcomponents. A bilateral Military Cooperation Center would be responsible for planning military operations, military exercises, logistics support, and intelligence exchanges, and assisting in the operation of the communication, command, control, and computer systems. It is unclear what role the U.N. Command, which the USFK Commander also holds, will have in the future arrangement. In 2014, South Korea's Minister of Defense reportedly announced that the goal was to transfer operational control (Opcon) in 2023, stressing the completion of the Korean Air and Missile Defense System (KAMD) by 2020 as an important step in the transfer process. To that effect, the Ministry of Defense announced that $1.36 billion would be invested in the KAMD system in 2017. In 2010, the Opcon transfer was postponed to 2015 after a series of provocations from North Korea and amid concerns about whether South Korean forces were adequately prepared to assume responsibility. As the new deadline of 2015 grew closer, concerns again emerged about the timing. Reportedly, South Korean officials worried that their military was not fully prepared to cope with North Korean threats and that Pyongyang might interpret the Opcon transfer as a weakening of the alliance's deterrence. Some military experts expressed concern that turning over control would lead to the United States reducing its overall commitment to South Korean security. Questions have also arisen over whether the ROK ground-centric military can effectively lead in a joint and coalition warfighting environment. In October 2014, the United States and South Korea announced in a joint statement that the allies would take a "conditions-based approach" to the Opcon transfer and determine the appropriate timing based on South Korean military capabilities and the security environment on the Korean Peninsula. The decisions to delay the Opcon transfer could be interpreted either as flexible adjustments to changed circumstances on the Korean Peninsula or as emblematic of problems with following through on difficult alliance decisions. In testimony to Congress in April 2015, then-USFK Commander General Curtis Scaparrotti explained the three general conditions for Opcon transfer: South Korea must develop the command and control capacity to lead a combined and multinational force in high-intensity conflict, South Korea must improve its capabilities to respond to the growing nuclear and missile threat in North Korea, and the Opcon transition should take place at a time that is conducive to a transition. Scaparrotti stated that main areas of attention for improving South Korea's capabilities will be C4 (command, control, computers, and communication systems), BMD, munitions, and ISR (intelligence, surveillance, and reconnaissance) assets. As a result, reportedly the Opcon transfer may not occur until 2020 or later. South Korea's Ministry of National Defense (MND) 2016 White Paper says that the MND will do its utmost to fulfill all necessary requirements to facilitate Opcon transfer by the mid-2020s by making progress toward being able to lead alliance military drills and organizing the potential future headquarters for CFC after the transfer is complete. Appendix B. DPRK, ROK, and U.S. Military Capabilities Complementing the narrative in Appendix A , the table below illustrates some of the differences in force structure between the DPRK and the U.S./Republic of Korea. Appendix C. U.S. Posture in the Pacific Theater

Summary: North Korea's apparently successful July 2017 tests of its intercontinental ballistic missile capabilities, along with the possibility that North Korea (DPRK) may have successfully miniaturized a nuclear warhead, have led analysts and policymakers to conclude that the window for preventing the DPRK from acquiring a nuclear missile capable of reaching the United States is closing. These events appear to have fundamentally altered U.S. perceptions of the threat the Kim Jong-un regime poses to the continental United States and the international community, and escalated the standoff on the Korean Peninsula to levels that have arguably not been seen since 1994. A key issue is whether or not the United States could manage and deter a nuclear-armed North Korea if it were to become capable of attacking targets in the U.S. homeland, and whether taking decisive military action to prevent the emergence of such a DPRK capability might be necessary. Either choice would bring with it considerable risk for the United States, its allies, regional stability, and global order. Trump Administration officials have stated that "all options are on the table," to include the use of military force to "denuclearize"—generally interpreted to mean eliminating nuclear weapons and related capabilities from that area. One potential question for Congress is whether, and how, to employ the U.S. military to accomplish denuclearization, and whether using the military might result in miscalculation on either side, or perhaps even conflict escalation. Questions also exist as to whether denuclearization is the right strategic goal for the United States. This is perhaps because eliminating DPRK nuclear or intercontinental ballistic missile (ICBM) capabilities outside of voluntary denuclearization, and employing military forces and assets to do so, would likely entail significant risks. In particular, any move involving military forces by either the United States/Republic of Korea (U.S./ROK) or the DPRK might provoke an escalation of conflict that could have catastrophic consequences for the Korean Peninsula, Japan, and the East Asia region. In this report, CRS identifies seven possible options, with their implications and attendant risks, for the employment of the military to denuclearize North Korea. These options are maintaining the military status quo, enhanced containment and deterrence, denying DPRK acquisition of delivery systems capable of threatening the United States, eliminating ICBM facilities and launch pads, eliminating DPRK nuclear facilities, DPRK regime change, and withdrawing U.S. military forces. These options are based entirely on open-source materials, and do not represent a complete list of possibilities. CRS cannot verify whether any of these potential options are currently being considered by U.S. and ROK leaders. CRS does not advocate for or against a military response to the current situation. Conservative estimates anticipate that in the first hours of a renewed military conflict, North Korean conventional artillery situated along the Demilitarized Zone (DMZ) could cause tens of thousands of casualties in South Korea, where at least 100,000 (and possibly as many as 500,000) U.S. soldiers and citizens reside. A protracted conflict—particularly one in which North Korea uses its nuclear, biological, or chemical weapons—could cause enormous casualties on a greater scale, and might expand to include Japan and U.S. territories in the region. Such a conflict could also involve a massive mobilization of U.S. forces onto the Korean Peninsula, and high military casualty rates. Complicating matters, should China choose to join the conflict, those casualty rates could grow further, and could potentially lead to military conflict beyond the peninsula. Some analysts contend, however, that the risk of allowing the Kim Jong-un regime to acquire a nuclear weapon capable of targeting the U.S. homeland is of even greater concern than the risks associated with the outbreak of regional war, especially given Pyongyang's long history of bombastic threats and aggressive action toward the United States and its allies and the regime's long-stated interest in unifying the Korean Peninsula on its terms. Estimating the military balance on the peninsula, and how military forces might be employed during wartime, requires accounting for a variety of variables and, as such, is an inherently imprecise endeavor. As an overall approach to building and maintaining its forces, the DPRK has emphasized quantity over quality, and asymmetric capabilities including weapons of mass destruction and its special operations forces. The Republic of Korea, by contrast, has emphasized quality over quantity, and maintains a highly skilled, well-trained, and capable conventional force. Most students of the regional military balance contend that overall advantage is with the U.S./ROK, assuming that neither China nor Russia become involved militarily. Should they do so, the conflict would likely become exponentially more complicated. As the situation on the Korean Peninsula continues to evolve, Congress may consider whether, and if so under what circumstances, it might support U.S. military action. Congress could also consider the risks associated with the possible employment of military force on the Korean Peninsula against North Korea; the efficacy of the use of force to accomplish the Trump Administration's strategic goals; whether and when a statutory authorization for the use of U.S. forces might be necessary, and whether to support such an authorization; what the costs might be of conducting military operations and postconflict reconstruction operations, particularly should a conflict on the Korean Peninsula escalate significantly; the consequences for regional security, regional alliances, and U.S. security presence in the region more broadly; and the impact that renewed hostilities on the Korean Peninsula might have for the availability of forces for other theaters and contingencies.