To determine the number and type of nuclear weapon limitations, we reviewed each weapon’s current MAR and associated NNSA guidance. We then interviewed officials from NNSA and the national laboratories to obtain clarification on technically complicated limitations. NNSA and DOD do not group limitations into types or categories. However, in order to report unclassified weapon limitation information in this report, we developed categories for types of limitations based on the MAR information. Using content analysis methodology, two analysts independently assessed each limitation and coded it as a certain type of limitation. To determine DOD officials’ concerns with the limitations’ impact for nuclear weapon operations, maintenance, and war planning, we interviewed officials in the Office of the Deputy Assistant Secretary of Defense for Nuclear Matters, Navy and Air Force lead project officers from each weapon’s Project Officer Group and interviewed and received briefings from officials in STRATCOM’s Joint Functional Component Command For Global Strike, the entity responsible for preparing and maintaining the nation’s nuclear war plan. In addition, we reviewed and analyzed the last five annual assessment reports (fiscal years 2006 to 2010) to determine what limitations the STRATCOM Commander reported. We also interviewed the current chairman of a technical advisory group who is responsible for completing the majority of the STRATCOM Commander’s annual assessment report and reviewed prior GAO work on the annual assessment process. To determine what, if any, mitigation actions DOD and NNSA currently engage in or plan to complete to address nuclear weapon limitations, we reviewed NNSA guidance and interviewed NNSA, national laboratory, and DOD officials. To determine how NNSA manages and reports on nuclear weapon limitations, we reviewed (1) established procedures governing the MAR development and revision process, (2) NNSA guidance on nuclear weapon limitations, and (3) documents associated with an ongoing joint DOD/NNSA review of nuclear weapon military requirements. We compared the documents with the Standards for Internal Control in the Federal Government. To determine if certain nuclear weapon limitations were potentially no longer applicable, we compared limitations with the most current information related to corrective actions as well as the current applicability of military requirements, as reported by NNSA guidance on limitations and officials from NNSA, the national laboratories, and DOD. To determine the extent to which NNSA has taken actions to address its recommendations on its surveillance program, we reviewed NNSA’s draft October 2010 management review and analyzed key NNSA documentation related to implementation efforts. This documentation includes a draft version of NNSA’s surveillance program manual; charters establishing the roles and responsibilities for entities responsible for managing the program; draft project management tools; and newly established procedures for establishing, executing, and tracking surveillance testing requirements. In addition, we interviewed key NNSA personnel, including the acting senior technical advisor for surveillance, about NNSA’s planned efforts to address its recommendations. We also compared NNSA’s actions against the federal standards for addressing recommendations from management reviews contained in the Standards for Internal Control in the Federal Government and Office of Management and Budget (OMB) Circular No. A-123, Management’s Responsibility for Internal Control. To determine the national laboratories’ role in the surveillance program, we conducted site visits, toured select facilities used to conduct surveillance tests, interviewed officials, and received briefings from officials at LLNL and SNL.information in writing from LANL. We conducted our work from October 2010 to February 2012 in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives. NNSA’s Office of Defense Programs is responsible for the manufacture, maintenance, refurbishment, surveillance, and dismantlement of nuclear weapons. Most modern nuclear weapons consist of three sets of components—a primary, a secondary, and a set of nonnuclear components enclosed in a case. When detonated, the primary and secondary components, which together are referred to as the weapon’s “nuclear explosive package,” produce the weapon’s explosive force, or “yield.” LANL, located in Los Alamos, New Mexico, and LLNL, located in Livermore, California, have design responsibility for the nuclear explosive package. SNL, located in Albuquerque, New Mexico, and Livermore, California, has design responsibility for nonnuclear components. Some nonnuclear components—collectively called “limited-life components”— have shorter service lives than the weapon itself and, therefore, must be periodically replaced. The U.S. nuclear weapons stockpile consists of eight weapons systems. Table 1 shows the weapon systems in the U.S. nuclear stockpile, their dates of entry into the stockpile, and the laboratories and military services responsible for each system. In February 2007, we reported on the process that DOD and DOE have established for fulfilling the annual assessment of the safety, performance, and reliability of the nation’s nuclear stockpile.STRATCOM Commander’s annual assessment of the nuclear stockpile is based primarily on the advice of a technical advisory group and provides an operational perspective; (2) the technical advisory group holds an annual conference where each entity involved in managing the stockpile—national laboratories, Project Officer Groups, NNSA, and DOD—present briefings to provide a complete perspective on the various issues affecting the stockpile; and (3) the laboratory director’s annual assessment is derived primarily from ongoing activities associated with NNSA’s Stockpile Stewardship Program, such as the results of weapon system and component level tests conducted We found that (1) the by NNSA’s stockpile surveillance program as well as data that provides an assessment of a weapon’s current reliability. NNSA’s stockpile surveillance program comprises the Core Surveillance Program and the Enhanced Surveillance Campaign, which are funded separately. Under the Core Surveillance Program, the national laboratories and production plants evaluate weapons and weapon components for the attributes of function, condition, material properties, and chemical composition through the following: System-Level Laboratory Testing. For such tests, units from each stockpiled weapon are chosen annually, either randomly or specifically, and sent to the Pantex Plant for disassembly, inspection, reconfiguration, and testing by the national laboratories. System-Level Flight Testing. These tests drop or launch a weapon with its nuclear material removed. NNSA coordinates flight testing with DOD, which is responsible for providing the military assets (e.g., aircraft and missiles) needed to drop or launch a weapon. Component and Material Testing. These tests are conducted on nuclear and nonnuclear components and materials by both the national laboratories and the production plants that manufactured them. NNSA defines campaigns as technically challenging, multiyear, multifunctional efforts to develop and maintain the critical capabilities needed to continue assessing the safety and reliability of the nuclear stockpile without underground testing. tomography (CT) image analysis tool for a particular nuclear component, which NNSA officials said they believe will enhance its ability to identify potential defects or anomalies. NNSA plans to conduct approximately 30 of these CT component tests in fiscal year 2012 under Core Surveillance, according to planning documents. Figure 1 shows the interrelationships among the segments of NNSA’s Stockpile Surveillance Program. For all U.S. nuclear weapons in the current nuclear stockpile, NNSA identified 52 weapon limitations, and of these, the majority fall into six types. DOD officials told us that a few limitations are a concern due to the potential impact on DOD weapon operation, maintenance, and war planning, but these officials also said that current and planned mitigation actions generally address their concerns with weapon limitations. We found that NNSA guidance to DOD on some limitations contains incomplete information, and DOD officials told us that the way NNSA communicates the potential impact of limitations on nuclear weapon operation, maintenance, and war planning is sometimes unclear. Furthermore, the national laboratories identified four existing weapon limitations (8 percent of all limitations) that are no longer valid—because, among other things, corrective action to address the limitation is complete—while some limitations will remain in effect until DOD changes potentially outdated military requirements. We characterized the 52 limitations that NNSA identified for all U.S. nuclear weapons into 10 types of limitations based on our analysis of each weapon’s MAR and associated guidance documents as well as through interviews with officials from NNSA, the national laboratories, and DOD. Eighty-six percent of these limitations fall into 6 types: detonation safety under abnormal conditions, weapon reliability, weapon delivery, more frequent replacement of limited life components, nuclear yield, and worker safety. According to DOD officials, a large majority of these weapon limitations do not impact DOD nuclear weapon operation, maintenance, and war planning activities. However, some DOD officials expressed concerns to us over the impact of a few weapon limitations, such as increased maintenance costs or additional issues to consider when developing war plans. For most limitations about which they raised concerns, DOD officials told us that current DOD mitigation actions, as well as the successful completion of ongoing and planned NNSA efforts, should address these concerns. DOD officials stated that the current stockpile allows sufficient flexibility to mitigate limitations. However, they told us there may be less flexibility in the future as the stockpile continues to age and decreases in size. Moreover, officials at one national laboratory told us that a smaller stockpile may not be able to support required mitigation actions if additional limitations, especially those that result in large decreases to weapon reliability, are identified in the future. The 2010 Nuclear Posture Review states that the United States is currently considering future stockpile reductions that would be based on a variety of factors, including the continuing implementation of NNSA’s Stockpile Stewardship Program.nuclear weapon limitations and the percentage of those limitations by type.