Global defense posture is an enabler of U.S. defense activities and military operations overseas and is a central means of defining and communicating U.S. strategic interests to allies, partners, and adversaries. It is driven by a hierarchy of national-level and DOD-specific guidance, which includes the National Defense Strategy and the National Military Strategy. Under DOD Instruction 3000.12, global defense posture includes three elements: Forces: forward stationed or rotationally deployed forces, U.S. military capabilities, equipment, and units (assigned or allocated). Footprint: networks of U.S. foreign and overseas locations, infrastructure, facilities, land, and prepositioned equipment. Agreements: treaties and access, transit, support, and status- protection agreements and arrangements with allies and partners that set the terms regarding the U.S. military’s presence within the territory of the host country. EUCOM is one of six geographic combatant commands and is responsible for missions in all of Europe, large portions of Asia, parts of the Middle East, and the Arctic and Atlantic Oceans (see figure 1). EUCOM evaluates the adequacy of posture in Europe to support relevant plans and achieve military objectives. EUCOM shares responsibility with the Chairman of the Joint Chiefs of Staff and the Office of the Secretary of Defense for U.S. military relations with allies and partners in Europe and the North Atlantic Treaty Organization (NATO). The number of U.S. military sites located in EUCOM’s area of responsibility and the number of military personnel assigned to Europe have decreased substantially since the end of the Cold War, and two heavy combat brigades had been deactivated by the end of fiscal year 2014. As of May 2016, EUCOM supported one airborne infantry brigade and one Stryker brigade, as well as approximately 62,000 military personnel across approximately 250 sites. Since 2009, we have reported on issues related to DOD’s efforts to estimate and report on the total cost of its global defense posture. In 2009, we identified weaknesses in DOD’s approach for adjusting its global defense posture and recommended, among other things, that DOD issue guidance for estimating total costs for global defense posture and modify its annual report to Congress to include the total cost to complete each planned posture initiative. In February 2011, we reported that EUCOM lacked comprehensive cost data in a key posture planning document and that therefore decision makers lacked critical information that they needed to make fully informed posture decisions. We recommended that the Chairman of the Joint Chiefs of Staff revise the Joint Staff’s posture planning guidance to include direction on how the combatant commands should analyze costs and benefits when considering changes to posture and to require that posture plans include comprehensive cost estimates. DOD agreed with the recommendations in both reports and subsequently took steps to implement them. In June 2012, we reported that DOD did not fully understand the cost implications of two posture initiatives in Europe—including its decision to return two heavy brigades from Europe to the United States—and that key posture planning documents did not completely and consistently include cost data. We recommended that DOD fully estimate the cost implications of these two initiatives, clarify components’ roles and responsibilities for estimating costs, and develop a standard reporting format for cost data. DOD generally agreed with our recommendations and has taken steps to implement two of them. Following the President’s June 2014 announcement of ERI, EUCOM identified five lines of effort that it would pursue under ERI, as described in table 1. Three of ERI’s lines of effort are expected to enhance DOD’s posture in Europe. For example, DOD is using ERI to increase the forces present in Europe by rotating an armored brigade combat team and elements of a combat aviation brigade to Europe every nine months. DOD also plans to enhance its footprint in Europe by using ERI funding to make infrastructure improvements and establish locations for prepositioned equipment. Finally, in order to implement ERI’s lines of effort and support U.S. activities, DOD is partnering with the State Department to negotiate host nation agreements that, among other things, establish protections for U.S. military personnel and provide DOD the authority to improve host nation installations and infrastructure. DOD is also supporting additional exercises and training to improve interoperability with partner countries while providing them with the capability and capacity to defend themselves, but these efforts are not expected to affect DOD’s long-term posture in Europe. Since 2014, DOD has expanded ERI’s objectives, increased its funding, and planned enhancements to posture in Europe. In fiscal years 2015 and 2016, ERI’s objective was to provide short-term reassurance to allies, and the initiative had little funding for long-term enhancements to posture. DOD focused its efforts on bolstering the security and capacity of NATO allies and partners by funding training, conducting exercises, and temporarily rotating Army and Air Force units to Eastern Europe. In fiscal year 2017, DOD expanded ERI’s objectives to include deterring Russian aggression in the long term and developing the capacity to field a credible combined force should deterrence fail. Recognizing that ERI’s expanded objectives would require DOD to alter its posture in Europe, DOD has requested increased ERI funding. DOD will have requested approximately $4.5 billion in ERI funding for posture enhancements through the end of fiscal year 2017; about $3.2 billion of this was requested for use in fiscal years 2017. During the time of our review, EUCOM had identified a need for additional funding over the next several years for additional posture enhancements in Europe. Specific details about EUCOM’s future posture plans and funding requirements were omitted because they are classified. DOD has requested increased funding to support planned enhancements to all three posture elements—forces, footprint, and agreements—in Europe: Force deployments to Eastern Europe: In fiscal years 2015 and 2016, the Army deployed armored brigade combat teams to Eastern Europe to provide short-term reassurance to allies and partners, which DOD officials said included Estonia, Latvia, Lithuania, and Poland, among other countries. These short-duration deployments were intermittent and focused on demonstrating U.S. commitment to allies and partners. Additionally, the Air Force deployed air units on 4- month rotations to help protect allies’ and partners’ air space. In the fiscal year 2017 budget justification materials provided to Congress, as ERI’s objectives expanded, DOD requested funding to retain Air Force fighter units in Europe. It also began deploying a rotational armored brigade combat team so that one such brigade would be present in Europe at all times (see figure 2). The first deployment, in January 2017, included approximately 4,000 personnel, 90 Abrams tanks, 90 Bradley Infantry fighting vehicles, and 112 supporting vehicles. Additionally, DOD began procuring and prepositioning equipment for two planned armored brigades in Europe, one of which will include modernized tanks, as an additional deterrent. According to Army officials, these force enhancements in Europe give the Army the ability to quickly deploy a substantial ground force in the event of a conflict. As of April 2017, DOD was still evaluating force enhancements in Europe as part of its fiscal year 2018 budget submission. Specific details were omitted because they are classified. New locations and improvements to infrastructure: Since ERI was announced in 2014, DOD has established new enduring locations in Europe. An enduring location is designated by DOD and is a geographic site that DOD expects to access and use to support U.S. security interests for the foreseeable future. During our review, DOD had not yet determined whether additional enduring locations would be needed to support ERI. In addition to establishing new enduring locations, DOD plans to improve installations and infrastructure. From fiscal years 2015 through 2017, DOD requested funding in its budget justification submissions to Congress for major military construction projects in nine European countries and to improve support infrastructure—such as roads, railheads, and airbasing—at these locations. Major military construction projects are those projects specified in National Defense Authorization Acts. During the time of our review, DOD was considering addition improvements to existing infrastructure, specific details of which are classified. According to DOD and State Department officials, DOD is also working with U.S. allies and partners to determine what infrastructure improvements to roads, railroads, and bridges need to occur outside enduring locations to allow rapid response to a conflict. New host nation agreements: Since ERI was announced, DOD and the State Department have completed host nation agreements with six European nations in support of ERI efforts: Romania, Bulgaria, and Poland, implementing previous agreements, in order to facilitate U.S. construction on installations and areas in the host country (June and July 2015 and June 2016). Estonia, Latvia, and Lithuania, providing an overarching framework for protections for U.S. personnel and U.S. access to installations in host nations (January 2017). DOD is using a separate process instead of its established posture planning process to plan for ERI’s posture initiatives because of the emergent nature of ERI requirements and their having been funded through the OCO budget. DOD has established global defense posture management and base budget development processes that plan for posture initiatives and collectively support the department’s efforts to establish priorities, evaluate resource requirements, and develop strategy and policy. As a result of its not using its established processes, DOD is not prioritizing posture initiatives funded under ERI against posture initiatives funded through its base budget, estimating these initiatives’ long-term sustainment costs, or communicating their future costs to Congress. DOD is planning ERI posture initiatives outside of its established processes and is funding these enduring initiatives—including rotational deployments and infrastructure projects—out of its OCO budget. We have previously identified risks associated with DOD’s practice of completing construction projects outside of its established processes. For example, in September 2016 we reported that DOD had not issued implementing guidance to establish a formal process for reevaluating ongoing contingency construction projects when missions change and that as a result DOD risked completing unnecessary construction projects. We also found that DOD lacked visibility into the amount of funding it was spending on operations and maintenance-funded construction projects in U.S. Central Command and that this increased financial risk and duplication risk for the department. Like U.S. Central Command, EUCOM is using DOD’s OCO budget to fund construction projects and is planning those projects outside of its established processes. Based on our analysis, DOD plans to spend approximately $503 million from fiscal year 2015 through the end of fiscal year 2017 on ERI-related construction projects—about $279 million for major military construction projects and $224 million for minor military construction and facilities maintenance and repair projects (hereafter, minor construction and repair), as shown in table 2. DOD has established global defense posture management and base budget development processes that plan for posture initiatives and collectively support the department’s efforts to establish priorities, evaluate resource requirements, and develop strategy and policy. According to DOD Instruction 3000.12, DOD’s global defense posture processes apply to DOD forces, footprint, and agreements that support joint and combined global operations and plans in foreign countries. According to the instruction, DOD’s components use these processes to address planning for global defense posture, resource requirements, and policy development, among other things. Further, it states that these processes are overseen by an executive council that provides recommendations, inputs, and expertise on global defense posture to key national strategy products. DOD’s Planning, Programming, Budgeting, and Execution Process serves as the annual resource allocation process for DOD and is intended to enable DOD to align resources to prioritized capabilities; balance necessary warfighting capabilities with risk, affordability, and effectiveness; and provide mechanisms for making and implementing fiscally sound decisions in support of the national security strategy and the national defense strategy. DOD is using a separate and evolving process to plan ERI’s posture initiatives—rather than following its established processes—because ERI is being funded through DOD’s OCO budget. According to officials from the Office of the Secretary of Defense, Cost Assessment and Program Evaluation, the department has recognized that the short-term planning process used to develop DOD’s OCO budget can create problems when it is used to plan for enduring initiatives. As a result, DOD has developed a separate process to plan for ERI. As part of the fiscal year 2018 planning process, EUCOM provided a prioritized list of potential requirements and an estimate of its annual costs by appropriation account to the Director for Cost Assessment and Program Evaluation. According to officials from the Office of the Secretary of Defense, Cost Assessment and Program Evaluation, DOD completed its review and provided recommendations to DOD’s senior leaders for approval in October 2016 and final decisions were made within DOD in April 2017. The specific criteria by which DOD assessed EUCOM’s potential requirements are classified. DOD is requesting funds for ERI’s posture initiatives as part of its OCO budget, which is generally intended to be short-term funding for ongoing contingency operations. In February 2009, the Office of Management and Budget, in collaboration with DOD, issued criteria to assist in determining whether funding properly belonged in DOD’s base budget or in its OCO budget. These criteria were updated in September 2010 and currently indicate that funding requests should be for specific geographic areas where combat or direct combat support operations occur (such as Iraq and Afghanistan). Further, budget items must meet other criteria. For example, OCO funding requests may be for constructing facilities and infrastructure in the theater of operations in direct support of combat operations. In these cases, the level of construction should be the minimum needed to meet operational requirements, and construction completed at enduring locations must be tied to surge operations or major changes in operational requirements. In January 2017, we reported that DOD did not apply the OCO criteria to ERI prior to deciding to budget for its requirements using its OCO budget. We recommended that DOD, in consultation with the Office of Management and Budget, reevaluate and revise the criteria for determining what can be included in OCO budget requests. DOD concurred with our recommendation and noted that it plans to propose revised OCO criteria. As of May 2017, the department has not implemented our recommendation. DOD’s planning for ERI’s posture initiatives does not establish priorities for ERI initiatives relative to those in the base budget, estimate long-term sustainment costs for some posture initiatives funded under ERI, or communicate future ERI costs to Congress. When planning ERI’s posture initiatives, DOD establishes priorities among ERI’s initiatives but does not review posture initiatives funded under ERI relative to those funded in the military services’ base budgets. DOD’s posture management process is intended to establish priorities among global posture elements and is overseen by a Global Posture Executive Council. According to DOD Instruction 3000.12, the Executive Council is responsible for reviewing, prioritizing, and endorsing across the combatant commands key posture elements such as military construction projects and international agreements. The Executive Council’s endorsements inform the military services’ budget deliberations. For the fiscal year 2017 ERI budget, EUCOM requested funding for several posture initiatives, including the continuous, rotational deployment of an armored brigade combat team and the establishment of prepositioned equipment in Europe. Officials representing the Under Secretary of Defense for Policy and the Director, Cost Assessment and Program Evaluation said that as part of its planning process for ERI the Deputy’s Management Action Group evaluated and prioritized posture initiatives funded under ERI. However, DOD could not provide documentation that it had established priorities relative to posture initiatives funded through the base budget. Further, the Global Posture Executive Council did not review or prioritize posture initiatives funded under ERI relative to posture initiatives funded through DOD’s base budget. Similarly, as DOD prepared the fiscal year 2018 ERI budget request, the Global Posture Executive Council did not prioritize EUCOM’s proposed ERI posture initiatives relative to initiatives funded through DOD’s base budget. More detailed information about these proposals, and their potential funding requirements, are classified. According to officials from the Office of the Under Secretary of Defense for Policy and the Joint Staff, DOD did not prioritize posture initiatives funded under ERI against base-budget funded posture initiatives, because ERI is funded through DOD’s OCO budget—which does not directly affect the services’ base budgets. However, because it does not prioritize ERI initiatives against other initiatives funded through the base budget, DOD lacks an understanding of the relative importance of initiatives funded under ERI and may begin investing in projects that it would not support in the absence of funding from DOD’s OCO budget. For example, Army officials noted that if funding were to become unavailable in DOD’s OCO budget, the Army is unsure how initiatives funded under ERI would rank in importance relative to other posture initiatives funded in its base budget. Consequently, the Army would be forced to make critical—and potentially costly—decisions quickly and without a clear idea of which posture initiatives were most important to the department. In planning for posture initiatives funded under ERI, EUCOM and the military services have not fully estimated the long-term sustainment costs of ERI’s posture initiatives to establish prepositioned equipment and construct new facilities. DOD’s global defense posture guidance indicates that, when evaluating potential changes to posture, the combatant commands should work with the military services to estimate the full cost of planned posture initiatives, including sustainment costs. DOD’s guidance on economic analysis also notes the importance of understanding both the size and timing of costs. Finally, our prior work has demonstrated that comprehensive cost estimates of current and future resource requirements are critical to making funding decisions and assessing program affordability. DOD leadership emphasized throughout the fiscal year 2018 budget review process that the services would need to fund ERI posture sustainment costs through their respective base budgets, but DOD did not direct the services and EUCOM to estimate these costs as they would have under their established processes. Officials from the Office of the Secretary of Defense, Cost Assessment and Program Evaluation said that DOD leadership emphasized that the military services would need to fund all future sustainment costs for ERI projects from their base budgets. Based on DOD’s approach for calculating rough order sustainment costs, we determined that ERI sustainment costs for prepositioned equipment and construction could be substantial. Army and Air Force officials said that they were working to identify and incorporate these costs into future base budget submissions. DOD officials said that we correctly applied DOD’s approach for estimating sustainment costs, but noted that actual costs may be lower than the estimated costs, because the military services may not fully fund sustainment. Additionally, officials said that EUCOM is trying to negotiate burden sharing agreements with host nations; however, it is unclear whether these negotiations will be successful or how any resulting agreements would affect DOD’s future costs. Without comprehensive estimates of the sustainment costs for the prepositioned equipment and major military construction projects in Europe, DOD decision makers have been limited in their ability to evaluate the affordability of these initiatives. Further, in the absence of these estimates, the services have been limited in their ability to plan for costs in future budgets, because they have an incomplete understanding of the magnitude of those costs and of when they are likely to be incurred. The funding plan that DOD submits to Congress for ERI does not contain information about ERI’s future costs. This is in contrast to the way DOD submits its funding plan for its base budget, where DOD provides Congress with cost projections over a 5-year period, by appropriation, leaving Congress with a better understanding of how and when to allocate resources. In reviewing the fiscal year 2018 ERI request, the Director for Cost Assessment and Program Evaluation assessed future costs associated with posture initiatives funded under ERI. We previously reported that DOD was not developing enduring requirements funded through its OCO budget as part of its budget and programming process. Officials from the Office of the Under Secretary of Defense (Comptroller) and the Office of the Secretary of Defense, Cost Assessment and Program Evaluation told us that DOD has not been required to provide estimates for future OCO costs for ERI to Congress previously. An official from the Office of the Under Secretary of Defense (Comptroller) told us that DOD does not plan to provide these future costs to Congress along with its fiscal year 2018 ERI budget submission. Additionally, in preparing its posture requirements, EUCOM did not identify assumptions regarding host nation and NATO burden sharing. For example, officials from the Office of the Under Secretary of Defense for Policy said that DOD has submitted a request to the NATO Security Investment Programmé for $200 million in funding to build a facility in Poland to store Army equipment. Officials told us that, as a result, this construction project was identified as a lesser priority in EUCOM’s fiscal year 2018 request for funding. A senior Army officer told us that completion of a facility in Poland was critical to its plans in Europe. Officials from the U.S. Mission to NATO told us that as of July 2016 NATO had approved funding to complete preliminary architectural and engineering design for this project. Officials expect additional funding will be made available in July 2017 to complete final design and site preparation and the full cost of the project will be approved in early 2019. However, these officials noted that additional funding beyond what has been approved by NATO may be required to meet U.S.-specific requirements. Similarly, EUCOM officials said that they are working to identify opportunities to defray future costs through host nation contributions, but it is unclear how much funding—if any—host nations will provide moving forward. Congress has expressed interest in knowing the future costs of enduring activities being funded through DOD’s OCO budget. The Senate Appropriations Committee’s report accompanying a bill for DOD’s fiscal year 2015 appropriations stated that the committee does not have an understanding of enduring activities funded by the OCO budget. The committee further noted that there is a potential for risk in continuing to fund non-contingency-related activities through the OCO budget. Both GAO’s and other federal standards emphasize that agencies should provide complete and reliable information on the costs of programs externally, so that decision makers can make informed decisions when allocating resources. DOD has not provided Congress projections of future costs for posture initiatives funded under ERI because it is reviewing those requirements outside of its budget and programming processes, and DOD officials said that the department is not required to provide this information. As a result, DOD is limiting congressional visibility into the resources needed to achieve ERI’s objectives. If DOD does not provide Congress with projections of the future costs of posture initiatives funded under ERI and information on its assumptions pertaining to host nation support and burden sharing, it will continue to impede congressional visibility into the resources that are needed to fully implement these initiatives. Russia’s annexation of Crimea and the subsequent threat of further aggression led DOD to establish and later expand ERI’s objectives and enhance posture in Europe to support a new U.S. strategy toward Russia. DOD has requested funding for these enhancements using its OCO budget; however, the processes DOD uses to develop its OCO budget were not designed to plan for and fund long-term, enduring initiatives such as ERI. By following a separate planning process when funding ERI with OCO, DOD is taking on risk by not reviewing and prioritizing ERI posture plans against other posture initiatives, estimating the costs for sustaining ERI initiatives, and providing Congress with estimates of ERI’s future costs. DOD risks making decisions that lack a strategic vision in comparison to other DOD priorities and may fund initiatives that cannot be sustained over the long term. Furthermore, Congress is likely to face challenges in assessing DOD’s estimated costs for ERI and the affordability of initiatives funded under ERI over the long term. To better ensure that DOD can target resources to its most critical initiatives and establish priorities across its base budget and overseas contingency operations budget, we recommend that the Secretary of Defense prioritize posture initiatives under ERI relative to those funded in its base budget as part of its established posture-planning processes. (Recommendation 1) To better enable decision makers to evaluate the full long-term costs of posture initiatives under ERI, we recommend that the Secretary of Defense direct EUCOM and the military services to develop estimates for the sustainment costs of prepositioned equipment and other infrastructure projects under ERI and ensure that the services plan for these long-term costs in future budgets. (Recommendation 2) To support congressional decision making, we recommend that the Secretary of Defense provide to Congress, along with the department’s annual budget submission, estimates of the future costs for posture initiatives funded under ERI and other enduring costs that include assumptions such as those pertaining to the level of host nation support and burden sharing. (Recommendation 3) We provided a draft of the classified report to DOD for review and comment. DOD partially concurred with all three of our recommendations, and we have reproduced DOD’s comments on the classified report in appendix II. DOD also provided technical comments, which we incorporated as appropriate. DOD partially concurred with our first recommendation to use its established posture-planning processes to prioritize ERI’s posture initiatives relative to those funded in DOD’s base budget. In its comments, DOD stated that it will continue to prioritize the negotiation of international agreements supporting ERI through the Global Posture Executive Council, and that an on-going Strategic Review will inform ERI and guide both EUCOM and the services in their program planning efforts. These are positive steps. DOD also stated it will adjudicate its ERI-funded force requirements through its global force management process, adding that it will continue to resource OCO funds for ERI requirements until there is a sufficient increase in DOD’s base budget to do so. However, we continue to believe, as noted in our report, that DOD could improve its planning for posture initiatives funded under ERI, whether or not they are funded through OCO, by using DOD’s established posture planning processes. Although DOD’s global force management process directly affects overseas military posture in the near term, this process is not designed to evaluate long-term posture priorities. If DOD does not prioritize the forces and infrastructure projects funded under ERI against those funded using the military services’ base budgets, it will continue to lack an understanding of the relative importance of the posture initiatives funded under ERI. Without such an understanding, DOD increases the risk that the services will need to make critical and potentially costly decisions without a clear idea of which posture initiatives are most critical to the department. DOD partially concurred with our second recommendation that EUCOM and the military services develop estimates for future sustainment costs and plan for these costs in future budgets. In its comments, DOD stated that its components will continue to estimate the sustainment costs for prepositioned stocks and other infrastructure projects during DOD’s annual program and budget review process. DOD also commented that without additional topline base budget funding, some portion of the associated sustainment costs will need to be financed with OCO funds. However, as we noted in our report, neither the Army nor the Air Force has fully estimated these potentially significant future costs, nor had either service incorporated them into their future budgets. Using OCO funds would mark a departure from DOD leadership’s emphasis that the services would need to fund ERI posture sustainment costs through their respective base budgets. Additionally, not developing robust estimates for sustaining these initiatives could increase long-term fiscal risk for the department if DOD shifts more ERI-associated enduring costs into its OCO budget. In the absence of robust cost estimates and deliberate planning to address those costs in future budgets, DOD will continue to be limited in its ability to evaluate the affordability of posture initiatives funded under ERI, and the military services may not plan adequate funding to sustain posture investments in Europe. DOD partially concurred with our third recommendation, to provide Congress with estimates of the future costs for posture initiatives funded under ERI and information on any underlying assumptions, such as those pertaining to the level of host nation support and burden sharing. In its comments, DOD stated that it does not currently prepare a formal 5-year Future Years Defense Program for OCO-related costs. Moreover, DOD commented that it factors in host nation support and burden sharing when preparing budget estimates for Congress. However, DOD does not state whether it will begin to provide Congress future estimates and any underlying assumptions with its budget submission. It is critical that DOD increase congressional visibility into ERI’s future costs and its underlying assumptions to facilitate congressional oversight and reasonably ensure that initiatives can be sustained over the long-term. We are sending copies of this report to the appropriate congressional committees, the Secretary of Defense, and the Commander, U.S. European Command. In addition, the report is available at no charge on the GAO website at http://www.gao.gov. If you or your staff have any questions about this report, please contact me at (404) 679-1816 or pendletonj@gao.gov. Contact points for our Offices of Congressional Relations and Public Affairs may be found on the last page of this report. GAO staff who made major contributions to this report are listed in Appendix III. The Army and Air Force identified approximately $224 million in unspecified minor military construction and facilities maintenance and repair projects (hereafter, minor construction and repair) that were programmed or obligated for the European Reassurance Initiative (ERI) in fiscal years 2015 through 2017. This includes $157 million for minor construction and repair projects identified by the Army and nearly $67 million for minor construction and repair projects identified by the Air Force. According to U.S. European Command officials, Navy and Marine Corps construction projects funded under ERI were either major military construction or exercise-related construction projects. The tables below do not include Navy and Marine Corps exercise-related construction projects. Using the data provided by the military services, we compiled the programmed and obligated funding for these minor construction and repair projects by fiscal year, country, location, and project name in tables 3 and 4. The information in these tables was provided by U.S. Army Europe and U.S. Air Force Europe in response to our request for a list of minor military construction and repair projects. The data provided did not identify the appropriations used for each project. Accordingly, we have not conducted a review to examine whether funds were appropriately used for a given project. In addition to the contact named above, Kevin O’Neill, Assistant Director; Alex Winograd, Analyst-in-Charge; Scott Bruckner, Adrianne Cline, Martin De Alteriis, Joanne Landesman, Jennifer Leotta, Carol Petersen, Michael Shaughnessy, and Jena Sinkfield all made key contributions to this report.

Answer: In response to Russia's annexation of Crimea in March 2014, the President announced the ERI, to reassure allies in Europe of U.S. commitment to their security. This initiative has been funded using OCO appropriations, which Congress provides in addition to DOD's base budget appropriations. The Joint Explanatory Statement accompanying the Continuing Appropriations and Military Construction, Veterans Affairs, and Related Agencies Appropriations Act, 2017, included a provision for GAO to review matters related to ERI. In this report, we (1) describe changes in ERI's objectives, funding under ERI, and DOD's posture in Europe since 2014 and (2) evaluate the extent to which DOD's planning processes for posture initiatives funded under ERI prioritize those initiatives, estimate their long-term costs, and communicate their estimated costs to Congress. GAO analyzed DOD strategy documentation, budget and cost analysis guidance, budget justification materials, and cost and obligations data. GAO also interviewed knowledgeable officials within the Office of the Secretary of Defense, U.S. European Command, the military services, and the State Department. Since 2014, the Department of Defense (DOD) has expanded the European Reassurance Initiative's (ERI) objectives, increased its funding, and planned enhancements to European posture. DOD expanded ERI's objectives from the short-term reassurance of allies and partners to include deterring Russian aggression in the long term and developing the capacity to field a credible combined force should deterrence fail. With respect to funding, DOD will have requested approximately $4.5 billion for ERI's posture enhancements through the end of fiscal year 2017 (about $3.2 billion for fiscal year 2017 alone), and in July 2016 EUCOM identified funding needs for future posture initiatives. The expansion of ERI's objectives has contributed to DOD's enhancing its posture in Europe. Specifically, DOD has increased the size and duration of Army combat unit deployments, planned to preposition Army equipment in Eastern Europe, added new enduring locations (e.g., locations that DOD expects to access and use to support U.S. security interests for the foreseeable future), improved infrastructure, and negotiated new agreements with European nations. As of April 2017, DOD was considering further force enhancements under ERI as part of the department's ERI budget request. DOD also was reviewing whether new enduring locations to support ERI were needed and was considering other improvements to existing infrastructure. DOD's process for planning ERI has not established priorities among posture initiatives funded under ERI relative to those in its base budget, nor estimated long-term sustainment costs for some posture initiatives funded under ERI, nor communicated future costs to Congress. ERI is being planned using a separate process from DOD's established processes and is funded from DOD's overseas contingency operations (OCO) appropriations. GAO found several weaknesses: Lack of prioritization : DOD establishes priorities among ERI posture initiatives but has not evaluated them against base budget initiatives using its posture management process. As a result, DOD lacks an understanding of the relative importance of ERI initiatives and may be investing in projects that it will not continue should OCO funding become unavailable. Lack of sustainment costs : EUCOM and the military services have not fully estimated the long-term costs to sustain equipment and construction funded under ERI. Based on DOD's approach for calculating rough order sustainment costs, GAO determined that these costs could be substantial. DOD officials said that GAO correctly applied DOD's approach for estimating sustainment costs, but noted that actual costs may be lower, because the military services may not fully fund sustainment. In the absence of comprehensive estimates, DOD has been limited in its ability to assess affordability and plan for future costs. Not communicating future costs : DOD limits Congress's visibility into the resources needed to implement ERI and achieve its objectives because it does not include future costs in its ERI budget request. This is a public version of a classified report issued in August 2017. Information on specific posture planning, guidance, and budget estimates that DOD deemed to be classified have been omitted from this report. GAO recommends that DOD prioritize ERI posture initiatives against initiatives in its base budget, develop cost estimates for sustaining initiatives, and communicate future costs to Congress. DOD partially concurred with GAO's recommendations. GAO continues to believe that these recommendations are warranted.