The size of the Armed Forces is a topic of perennial congressional interest and debate, as each year Congress sets minimum and maximum strength levels for the active components (AC); and maximum strength levels for the reserve components (RC). The number of military personnel in each service is directly related to how many units of various types they can deploy for use in operational missions. The number of military personnel also affects the cost of the military. More personnel require additional funding for their pay and benefits; combined into units, they require additional funding for training, operations, equipment, maintenance, and travel. The number of military personnel also has a long-term impact on the cost of veterans benefits. The House and Senate versions of the National Defense Authorization Act (NDAA) for FY2017 authorized differing levels for active duty personnel in each of the services, but these authorizations diverge most significantly with respect to the Army. This report provides an overview of active duty Army personnel strength changes in recent years, highlights the factors which have contributed to these diverging approaches in the respective NDAAs, and outlines some factors which Congress may consider. Congress regulates the size of the Armed Forces by authorizing specific personnel strength levels in law each year. Active component "end strength" for the Army has changed substantially over the past several decades, as shown in Figure 1 . With the collapse of the Soviet Union and the end of the Cold War, Army personnel strength declined rapidly in the 1990s, levelling off at about 480,000 soldiers. Congress increased the Army's strength in response to the demands of wars in Iraq and Afghanistan, but began reversing those increases in light of the withdrawal of U.S. forces from Iraq in 2011, the drawdown of U.S. forces in Afghanistan beginning in 2012, and budgetary constraints. The end strength for the Army in FY2016, as established by Section 401 of the FY2016 National Defense Authorization Act, is 475,000 soldiers. For FY2017, the Administration proposed lowering the Army's end strength to 460,000. The Senate version of the FY2017 National Defense Authorization Act approved Army end strength identical to the Administration request, while the House version approved Army end strength of 480,000. The divergence between the Administration request and the House and Senate bills reflects differing assessments of a variety of factors, including operational tempo, budgetary constraints, and, most frequently, readiness (see text box below for a summary of these competing perspectives). Readiness is a term policymakers, analysts, and military leaders often use when describing the state of the U.S. military. The Department of Defense defines readiness as "the ability of military forces to fight and meet the demands of assigned missions." Army readiness evaluations revolve around four main components: personnel, equipment availability, equipment readiness, and training. The unit's overall readiness assessment—its ability to accomplish its core functions, provide its intended capabilities, and carry out its mission-essential tasks—is determined by the lowest rating of these four areas. As the lowest rating factor determines the overall readiness evaluation, an improvement in one area will not necessarily improve the overall readiness rating of a unit. Additionally, as the individual factors can influence each other (for example, increasing personnel in a unit without providing them sufficient training could improve the personnel rating but lower the training rating), one cannot necessarily make future readiness predictions based on projected improvement in one area. For a more detailed discussion of how the Army determines and reports unit readiness, see CRS Report R43808, Army Active Component (AC)/Reserve Component (RC) Force Mix: Considerations and Options for Congress , by [author name scrubbed] and [author name scrubbed]. As Congress continues to debate the appropriate size for the Army several considerations are particularly significant. These include the strategic environment, the role of the Army within this environment, how the Army might use additional end strength, the results of a congressionally directed study on the future of the Army, and the constraints of the Budget Control Act of 2011. Each of these topics is discussed in more detail below. For many observers, questions regarding the appropriate end strength of the Army are related to the changing international security landscape, and the perception that those changes are resulting in heightened threats to the United States and its interests abroad. For others, the cost of increasing the size of the Army is the predominant factor in the debate. The National Military Strategy (NMS), published in June 2015, describes a global environment marked by increasing interdependence, complexity, and the diffusion of information and technologies across state boundaries. The NMS organizes threats to the United States into two primary categories: "revisionist" states and "violent extremist organizations" (VEOs). With respect to "revisionist states," the NMS calls attention to the challenges posed by four different nations: Russia, Iran, North Korea, and China. Russia, it states, has demonstrated its willingness to redraw international boundaries and violate international law using military force. Further, the NMS states that Iran is a state sponsor of terrorism that has undermined stability in Israel, Lebanon, Syria, and Yemen. North Korea, according to the NMS, threatens its regional neighbors (including Japan and South Korea) with its production of nuclear weapons. Finally, the NMS argues that China's recent "land reclamation" (also referred to as "island building") activities in the South China Sea are destabilizing. With respect to VEOs, the NMS points out that these actors use a combination of low-technology weaponry (such as suicide vests and improvised explosive devices) as well as sophisticated propaganda and messaging strategies to spread their influence. While the NMS assesses the VEO threat as "immediate" due to the fact that they are currently destabilizing the Middle East, it also notes—for the first time in several decades—that the probability that the United States may find itself at war with another great power is "low but growing." The NMS also discusses "hybrid" warfare, whereby state and non-state actors (Russia and its Ukrainian proxies, for example) "blend techniques, capabilities, and resources to achieve their objectives." The ensuing ambiguity in the battle space makes it difficult for the United States and its allies to plan for, and coordinate, their responses. Indeed, as Director for National Intelligence James Clapper testified before the Senate Armed Services Committee, "[i]n my 50-plus years in the intelligence business, I don't—I cannot recall a more diverse array of challenges and crises that we confront as we do today." Although there is a general consensus that the global security environment is becoming significantly more challenging, the role that the U.S. military generally—and the Army specifically—ought to play in advancing U.S. interests is the subject of considerable debate. On the one hand, there are those who maintain that in the face of these myriad threats, the utility of ground forces will increase in the coming years. This is for a variety of reasons including (but not limited to) bolstering deterrent postures, prosecuting "grey zone" or "hybrid" warfare, providing enabling and logistical functions for the rest of the joint force, and prosecuting military campaigns in which terrain must be seized. First, moreso than remote or offshore military capabilities, the presence of ground forces can send unique political-military signals that can help deter adversaries and reassure allies. This is because the placement of ground forces abroad—which is, in essence, risking soldiers' lives—communicates a high degree of U.S. commitment to the pursuit of national strategic objectives. The Cold War provides a historical example of these dynamics playing out. As the logic went, if the Soviets initiated a conflict, the large numbers of American troops stationed across Europe meant that U.S. casualties would be inevitable. The loss of American life in Europe would, in turn, prompt a significant U.S. military response to repel a Soviet attack. This is why the presence of U.S. troops in Europe during the Cold War was viewed as critical to underscoring the overall deterrent posture in that theater—in addition to the other military capabilities, including nuclear weapons, the presence of U.S. troops signaled the credibility of U.S. security guarantees in theater. Second, as was demonstrated in Iraq (2003-2010), Afghanistan (2001-present), and the Balkans (1990-present) operations that take place among local populations, to include peacekeeping, stability operations, counterinsurgencies, and "hybrid" or "grey zone" conflicts, generally require a significant presence on the ground. This is because such operations often use personnel-intensive techniques such as patrolling, intelligence collection, and targeted strikes in order to create stability that can subsequently be translated into sustainable political outcomes. As one argument goes, higher troop numbers are required for contingencies in which U.S. forces must operate among indigenous communities. The Army's 2006 field manual on counterinsurgency notes that for past conflicts, troop numbers were based on the number of insurgents , suggesting that 10 to 15 troops per insurgent were needed to ensure success; but a better means to determine troop requirements based on inhabitants now suggests 20 troops per 1,000 residents is the minimum density needed for effective counterinsurgency operations. This leads to the third role for large portions of U.S. ground forces—providing enabling and logistical support for both combat and steady-state operations. These combat-support and/or combat service support functions include life support, headquarters staffing, and logistics. Even "light footprint" counterterrorism operations require supporting infrastructure, much of which is personnel intensive. As General McChrystal (ret.), former U.S. commander in Afghanistan, remarked in an interview with T he New York Times : Q: Can one maintain a counterterrorism capability in Afghanistan without a complementary counterinsurgency effort? A. If you take the raid into Abbotabad, that was years of gathering intelligence, some on the ground, some in the air, some signals intelligence. It was launched from bases — not just a single base, it needed a network. It had medevac [medical evacuation] available. It had this infrastructure that supported it that isn't seen by people who just look at a couple helicopters landing in a compound. CT [counterterrorism] typically requires that.... Otherwise, it's really, really hard. Indeed, the Army provides a number of enablers to the joint force that allow the U.S. military—and, at times, other agencies of the government—to conduct global operations. According to a study released by the Army War College, the Army currently has executive agency for 41 out of 84 enabling and logistical tasks that support two or more services. While some observers argue that the proportion of forces dedicated to logistical and enabling functions is out of balance with those actually performing operations (the so-called "tooth to tail ratio"), others counter that the logistical requirements for expeditionary forces are now highly complex, and that without medevac, intelligence, financial (such as the Commander's Emergency Response Program), and other enablers, deploying combat troops would be considerably more risky. Finally, ground forces are essential in those military operations wherein terrain must be seized and held. In recent campaigns, the United States generally has preferred to build the capacity of local forces in order to "hold" territory once it has been cleared. While these missions, in theory, require fewer ground forces than ones primarily conducted by U.S. forces, depending on the size of the training mission, this still can amount to a sizeable troop requirement. Currently, the United States has 3,870 troops in Iraq, the overwhelming bulk of which are focused on garrison-based, higher-level headquarters training of Iraqi Security Forces. Operation Resolute Support, the NATO mission in Afghanistan, currently comprises 12,930 troops who are entirely focused on training and equipping the Afghan Security Forces. Furthermore, given the NMS statement that there is a small but growing likelihood that the United States might find itself in a conflict with a major power, the United States must also plan and prepare for those contingencies in which U.S. forces must shoulder the majority of the combat burden in confronting major adversaries. This would likely require even more troops than those contingencies wherein the United States can operate "by, with and through," local forces, especially given recent advances in the lethality of the military forces of other major powers like Russia. On the other hand, the above arguments notwithstanding, other observers maintain that most of the functions listed above can be adequately performed with lower troop levels due to emerging technologies, tactical innovations, and military capability advancements. Proponents of this concept, which is often referred to as "transformation," or a "revolution in military affairs," maintain that special operations forces, combined with precision guided munitions, can have the kinds of decisive effects on the battlefield that used to be achieved through massive ground troop formations. Others believe that the Army is "overreacting" in its arguments for increased troop strength to meet the emerging strategic environment. Contrary to arguments that the Army would be overmatched in a contest with Russian forces, some maintain that "it is exceedingly unlikely the U.S. Army will ever be 'outranged and outgunned'" due to advances in joint warfare, and in particular, Air Force and Naval Air support to ground operations. Finally, some question whether the United States has the political appetite to engage in these kinds of ground-force-intensive contingencies in the future. As evidence, they refer to the 2012 Defense Strategic Guidance, which states that "U.S. forces will no longer be sized to conduct large-scale, prolonged stability operations." Indeed, as former Secretary of Defense Robert Gates said, "in my opinion, any future defense secretary who advises the president to again send a big American land army into Asia or into the Middle East or Africa should 'have his head examined,' as General MacArthur so delicately put it." Still, he went on to note, ...when it comes to predicting the nature and location of our next military engagements, since Vietnam, our record has been perfect. We have never once gotten it right, from the Mayaguez to Grenada, Panama, Somalia, the Balkans, Haiti, Kuwait, Iraq, and more—we had no idea a year before any of these missions that we would be so engaged. Another factor that Congress may consider when debating the appropriate Army strength level is how any additional personnel would be used by the Army. An increase in end strength would allow the Army to create new units or bolster the capacity of existing units. Nevertheless, Army leadership has not publicly provided specifics on how additional end strength would be used. While the Army has not offered much detail on how additional end strength might be used, it is reasonable to speculate it would not solely be used to create new units but also to add capacity to existing units and supporting organizations as well. In terms of new units, the National Commission on the Future of the Army—discussed later in this report—pointed out shortfalls in air defense; tactical mobility; missile defense; chemical, biological, radiological, and nuclear (CBRN) defense; field artillery; fuel distribution; water purification; Army watercraft; and military police. Additional end strength could result in the creation of additional units of these types. Other Army initiatives could also benefit from increased end strength. In June 2016, Army Chief of Staff General Mark Milley stated that the Army plans to stand up a number of Train, Advise, and Assist Brigades over the next four to five years. These brigades, manned primarily as "chain of command" units with officers and noncommissioned officers only, would serve a dual purpose to both deploy overseas to advise, assist, and help train partners and allies and also as a means to expand the Army in the case of emergency but adding soldiers to the brigade's existing chain of command to form a BCT. Furthermore, General Milley noted before the Senate Armed Services Committee on April 7, 2016, that "manning requires an appropriate mix of forces across the Army—Regular Army, Army National Guard, and the Army Reserve—to accomplish our national military objectives," suggesting that additional end strength decisions also need to consider Army force mix as well. Without knowing specifics on the types of units and organizations that would be the beneficiaries of an end strength increase—as well as what component—it is difficult to ascertain the impact on readiness. An important factor is that of operational tempo. If the Army is committed to additional operations or if troop levels in existing operations are increased, additional end strength could be helpful as General Milley has indicated. Perhaps one of the most important considerations of additional end strength is that of additional funding to support readiness. On February 24, 2016, when asked about a possible increase to Army end strength during a Senate Appropriations Committee hearing, General Milley reportedly stated "I think that having increased numbers would help out readiness, if and only if we had the money to support that." If end strength is increased but readiness funding is either inadequate or not provided, the Army could have difficulty paying for their training and equipment. Title XVII of the FY2015 NDAA established an independent commission to study Army strength and force structure and directed it to ... undertake a comprehensive study of the structure of the Army, and policy assumptions related to the size and force mixture of the Army, in order— (A) to make an assessment of the size and force mixture of the active component of the Army and the reserve components of the Army; and (B) to make recommendations on the modifications, if any, of the structure of the Army related to current and anticipated mission requirements for the Army at acceptable levels of national risk and in a manner consistent with available resources and anticipated future resources. The committee report which accompanied the Senate version of this NDAA explained the rationale for the commission as follows: The committee is aware that the Army and the Department of Defense continue their analysis, course of action development, and decisionmaking process with respect to the distribution of reductions of both end strength and force structure necessary to achieve the savings required by the Budget Control Act of 2011. The committee believes that under these circumstances an independent and objective review of Army size and force structure by a national commission is worthwhile. The commission would be required to submit a report to the congressional defense committees not later than February 1, 2016. The NCFA reported its findings to Congress and the Administration on January 28, 2016. The 208-page report contained 63 recommendations, many of which could have an impact on Army end strength. Major end strength-related recommendations are summarized below: An Army of 980,000 soldiers (Regular Army of 450,000; Army National Guard of 335,000; and an Army Reserve of 195,000) is the minimally sufficient force to meet current and anticipated missions with an acceptable level of risk. This finding is consistent with the end strength and force mix minimums established by Army leadership in 2014. The Army should retain an 11 th Regular Army Combat Aviation Brigade (CAB) instead of drawing down to 10 CABs as proposed under the Aviation Restructuring Initiative (ARI). The Army should convert the U.S. Army Europe administrative aviation headquarters to a warfighting mission command element similar to a CAB headquarters. Noting the security situations in Ukraine and Syria, concern was expressed that no short-range air defense battalions were in the Regular Army and a sizeable percentage of the National Guard's short-range air defense capability was devoted to protecting the National Capital Region, leaving little spare capacity for contingency operations. Shortfalls were identified in tactical mobility; missile defense; chemical, biological, radiological, and nuclear (CBRN) defense—particularly as it relates to homeland defense; field artillery; fuel distribution; water purification; Army watercraft; and military police. If the Army's 980,000 soldier strength cannot be increased to address the creation of units to address the aforementioned shortfalls, the Army should consider eliminating two Regular Army Infantry Brigade Combat Teams (IBCTs) to free up spaces to create these units. The Army should increase Armored Brigade Combat Team (ABCT) capacity based on current and projected threat environment. The Army should ensure Combatant Commands (COCOM) and Army Service Component Commands have the ability to provide operational mission command in proportion to the unique mission for each COCOM. Regarding the Army's proposed Aviation Restructuring Initiative (ARI), the commission recommended the Army maintain 24 manned AH-64 Apache battalions—20 in the Regular Army and 4 in the National Guard. To help decrease the costs to the commission's recommendation, only 2 UH-60 Black Hawk transport helicopter battalions would be added to the National Guard as opposed to the 4 Black Hawk battalions under the Army's ARI proposal. The NCFA's findings on shortfalls in air defense; tactical mobility; missile defense; chemical, biological, radiological, and nuclear (CBRN) defense; field artillery; fuel distribution; water purification; Army watercraft; and military police have potential implications for Army end strength. Depending on the Army's analysis, it could choose to create a number of units of varying size (likely ranging from company to brigade-sized) to address the aforementioned shortfalls as well as other recommendations such as an 11 th CAB or increased ABCT capacity. Required personnel aside, the creation of these units would likely not be done "immediately" but instead over a number of years, based on the perceived urgency of the capability shortfall and dependent on the availability of necessary weapon systems, combat vehicles, and equipment needed to outfit new units. The Army has three basic ways of creating new units or adding capacity to existing units—it can convert existing units to create new units or add capacity; it can deactivate existing units to free up personnel and equipment resources to create new units or add capacity; or it can ask for additional end strength and associated readiness funding to create new units or add capacity. Converting existing units considered excess or no longer relevant to perceived operational needs is considered the "easiest" option, and the Army did a significant number of unit conversions when it instituted Modularity in 2003 to meet rotational demands of the wars in Iraq and Afghanistan. Nevertheless, following the Army's significant downsizing since 2010, fewer units are likely candidates for conversion. In a similar manner, deactivating units to free up personnel and equipment resources for new units/additional capacity might also prove impractical, as evidenced by the Army's reluctance to deactivate two Regular IBCTs. Army leadership has indicated that the NCFA's recommendation of eliminating two Regular Army Infantry Brigade Combat Teams (IBCTs) to free up spaces to create new units is not practical or desired. The Army's report to the Department of Defense (DOD) on which NCFA recommendations it plans to implement was reportedly provided to the Secretary Defense in mid-April 2016. However, DOD's response has not yet been publically released. This being the case, additional end strength is an option to meet capability and capacity shortfalls. Finally, independent from the NCFA's recommendations, the Army might also have internally identified additional units or capacity that it believes are needed to meet current and projected national security needs that might also have an impact on Army end strength requirements. The Budget Control Act of 2011 (BCA) established statutory limitations on spending by imposing a series of caps on discretionary budget authority for defense and nondefense programs from FY2012 through FY2021. For FY2017, the BCA cap on defense spending limits the DOD military budget to $523.9 billion. The President's FY2017 budget request allocated the $523.9 billion in available funding across the military departments. The Army's share of the allocation, $123 billion, is distributed across appropriation titles (military personnel; operation and maintenance [O&M]; research, development, test and evaluation [RDT&E]; and military construction/other accounts) as depicted in Figure 2 . As indicated above, the Administration's request for a $523.9 billion military budget matches the BCA cap. Should Congress decide to increase the size of the Army beyond the level funded by the President's budget, the increase would need to be accompanied with an associated increase in budget authority for the Army or sufficient reductions from other Army accounts. Options for doing so are discussed below. In contemplating increased Army end strength, Congress may consider costs by type of Army unit the personnel may be assigned to. Doing so would account for variances in organizational structure (officer to enlisted ratios), training requirements, and assigned equipment requirements, which affect the annual average cost of the unit. For example, an active duty infantry brigade combat team (BCT) is typically comprised of about 4,230 personnel (mainly enlisted) and several hundred generally unarmored wheeled vehicles. The average annual direct cost per troop in such a brigade is estimated at $106,383. In comparison, an active duty Aviation Brigade is typically comprised of 3,020 personnel, many of whom are officers or warrant officers, and is outfitted with a fleet of helicopters and the associated support equipment. As result, the average annual direct cost per troop for an Aviation Brigade is estimated at $162,252 (or 53% more). See Table 2 for a comparison of average annual cost per troop by selected unit type. If an increase in the size of the Army is desired, Congress could raise or repeal the BCA caps, which it has done three times since the BCA was enacted in 2011. In 2012, 2013, and 2015 the limits on defense and nondefense spending were raised—each time adjusting only the limits for the two succeeding years. Figure 3 depicts the changes to the BCA limits on defense spending. Without an increase to the BCA limits, another alternative is to fund the increased force structure by designating it as an "emergency" or for "Overseas Contingency Operations/Global War on Terror" (OCO/GWOT) requirements. Doing so would exempt the funding from the BCA limits. This approach was supported by the House in passage of H.R. 4909 , the National Defense Authorization Act for Fiscal Year 2017. The measure provided an additional $18.0 billion in funding for base requirements of the DOD and designated the funding as OCO/GWOT for the purposes of the BBEDCA exemption. In addition to $1.6 billion in funding for Military Personnel in the Army (active and reserve components), H.R. 4909 also increased Army procurement, O&M, and RDT&E (see Table 3 ). This approach has been criticized by some, mainly because OCO funding is not a guaranteed source of funding in future years. Secretary of Defense Carter, in testimony before the Senate Appropriations Subcommittee on Defense, called the House proposal to fund base requirements out of OCO "deeply troubling and flawed" and went on to explain, "It buys force structure without the money to sustain it and keep it ready, effectively creating hollow force structure, and working against our efforts to restore readiness." Funding an increase to Army end strength through a reduction to the other military departments' budgets is another option; however, reducing funding to the other departments might have an adverse impact on their combat capabilities, readiness, and the joint force overall. The FY2017 Defense Budget Overview describes the rationale behind the President's request, which provided for an Army of 980,000 soldiers. With continuing fiscal and strategic uncertainty, the FY2017 budget request reflects the Department's responsible choices to develop a coherent defense program with the proper balance between capacity, capabilities, and current and future readiness....This budget adjusts programs that support joint force technological superiority, stabilizes total ground force end strength, funds important reforms of health care, retirement, and family programs, focuses on building the force of the future, and continues to make better use of defense resources through acquisition reform, management reform, and reducing lower priority programs to comply with the Bipartisan Budget Act. If increases to Army end strength were to be funded by reductions to the Department of the Air Force, the Department of the Navy, or both, Congress may consider risk to the joint force's ability to meet mission requirements in other areas, such as countering advanced anti-access and area-denial capabilities, nuclear deterrence, space, missile defense, cyber, precision strike, and special operations. Another option to pay for additional Army end strength would be to reduce Army spending in other areas, but this approach could have a negative impact on Army readiness, depending on where the spending reductions were applied. For example, then-Secretary of Defense Robert Gates warned an audience at the American Enterprise Institute in May 2011 about the potential for a "hollow force" if budget limitations are not applied in a manner that balances the size of the force with the readiness of the force: I am determined that we not repeat the mistakes of the past, where the budget targets were met mostly by taking a percentage off the top of everything, the simplest and most politically expedient approach both inside the Pentagon and outside of it. That kind of "salami-slicing" approach preserves overhead and maintains force structure on paper, but results in a hollowing-out of the force from a lack of proper training, maintenance and equipment—and manpower. That's what happened in the 1970s—a disastrous period for our military—and to a lesser extent during the late 1990s. Secretary Gate's comments are applicable in consideration of increasing the size of the Army while the BCA caps constrain availability of funds to train, equip, sustain, and modernize the larger force. General Joseph Dunford, Chairman of the Joint Chiefs of Staff, told the Senate Appropriations Subcommittee on Defense "To me, the number one priority that we have today is to make sure whatever size force we have is capable.... So, trying to achieve that balance [Senator] is really what this year has been all about." The National Commission on the Future Army raised similar concerns. Commenting on the President's FY2017 budget request in their final report, the commission cautioned: In this constrained budget environment, the Army prioritized manpower numbers and force readiness to hedge against near-term demands, accepting substantial risk in modernization. The Commission finds this solution regrettable but understandable; given the persistence of challenges to the United States and the ongoing strain those challenges are putting on ground forces.... Nevertheless...these risks to modernization cannot be sustained if the Army is to protect the mission readiness of the force in the long term. Another alternative to funding an increase in Army end strength without an increase in defense spending is to find "savings" in existing DOD activities. In its annual consideration of defense authorization and appropriation bills, Congress routinely identifies programs that are under-executing (carrying unobligated balances), economic factors such as changes in the cost of fuel and foreign currency fluctuations, and activities that can be deferred. Congress may consider targeted reductions such as those to fund—in whole or in part—a desired increase in the size of the Army. The Department of Defense plans further reductions in the size of the Army, proposing a FY2018 end strength of 450,000. To reconcile competing interpretations and judgments about the proper size of the Army, Congress may gather additional information from the Army and outside experts. Some key questions Congress may pose to them include include the following: Although the international security environment is arguably becoming more challenging and complex, the role of ground forces—relative to other services—in helping the nation meet those challenges is somewhat unclear. What are the tasks that the Army, specifically, needs to accomplish for the nation? Within a coalition context? On behalf of the other U.S. military services? Compounding matters, the United States has a somewhat precarious track record when attempting to predict the type and character of future conflicts. What might an agile Army force structure, capable of more rapidly adapting to future security challenges, look like? At present, it is not known what types of new units the Army would create should it be provided with additional end strength, making it difficult to assess the benefit of any additional strength. What would the Army do with additional end strength? Would it build new units and, if so, what types? Would it augment existing units and, if so, in what ways? How would these units enhance the capabilities or capacity of the Army to perform essential missions? What existing capability gaps would be addressed? How quickly would the Army be able to field these new or augmented units? How would such plans coincide with or conflict with congressional priorities for Army force structure? Additional military personnel generates costs beyond their pay and benefits. When combined into units, they require additional funding for training, operations, equipment, maintenance, and travel so they can effectively conduct their designated mission. What additional resources would be associated with creating new units or augmenting existing units—for example, equipment, training, facilities, and funding? Is there excess equipment that can be used or would there also be a requirement to procure new equipment and major weapon systems? How long would it take to equip and train new units? How much would this cost?

Summary: Article I, Section 8, of the U.S. Constitution vests Congress with broad powers over the Armed Forces, including the power "To raise and support Armies" and "To provide and maintain a Navy." As such, the size of the Armed Forces is a topic of perennial congressional interest and debate. Congress annually sets minimum and maximum strength levels for the active components and maximum strength levels for the reserve components. The House and Senate versions of the National Defense Authorization Act (NDAA) for FY2017 authorized differing levels for active duty personnel in each of the services, but these authorizations diverge most significantly with respect to the Army. The Senate version of the FY2017 National Defense Authorization Act approved Army end strength of 460,000 soldiers, while the House version approved an Army end strength of 480,000. The Senate figure represents a decrease of 15,000 soldiers in comparison to the Army's FY2016 end strength of 475,000, while the House figure represents an increase of 5,000. Congress's decision about the size of the Army for FY2017 will likely hinge on how it reconciles competing interpretations and judgments about key issues, including the current and emerging strategic environment; the role of the Army in advancing national security interests within that environment; how any additional end strength would be used by the Army; the results of a congressionally directed study on the future of the Army; and the trade-offs associated with various options to fund additional strength in the context of budgetary constraints. In addition to the decision for FY2017, the debate about the size of the Army may well continue into the next Congress, as the Department of Defense plans further reductions in the size of the Army, proposing FY2018 end strength of 450,000. There will also be a new President in January, and his or her policy priorities may revise the contours of this debate. This report provides an overview of active duty Army personnel strength changes in recent years, outlines the different end strength authorizations in the House and Senate versions of the FY2017 NDAA, highlights the perspectives which have contributed to these diverging approaches in the respective NDAAs, and outlines some factors which Congress may consider as it determines the appropriate size for the Army.