DOD Instruction 4151.20, Depot Maintenance Core Capabilities Determination Process, requires the military services to apply a methodology to determine their core capability requirements—that is, to identify what core capabilities are required and what workload would be necessary to enable them to sustain these core capabilities at the depots. DOD’s instruction also requires the military services to determine the estimated cost of workloads to sustain the core capability requirement. The instruction describes a series of mathematical computations and adjustments that the military services are required to use to compute their core capability requirements, and to identify the projected workload needed to support these requirements. Specifically, the instruction requires that the military services identify the weapon systems required to execute the Chairman of the Joint Chiefs of Staff’s strategic and contingency plans, which, among other things, guide the use and employment of the military forces across all geographic regions and sustain military efforts over different durations of time. After the systems are identified, the military services compute annual depot maintenance capability requirements for peacetime, in direct labor hours, to represent the amount of time they will regularly take to execute required maintenance. A military service may adjust calculated direct labor hours to address redundant capability requirements that are so similar to one another that they share common base repair processes. DOD tracks core capability requirements using the following two metrics: direct labor hours, each of which represents 1 hour of effort directly allocated to a category of work; and work breakdown structure categories, which bundle types of work according to weapon systems and equipment. DOD uses work breakdown structure categories to organize data on its various core capability requirements and workloads, as well as to manage and report on its core capabilities. There are 10 first-level work breakdown structure categories, and these in turn are broken down into second-level subcategories, which are the major elements that make up the system or equipment in the first-level category. Figure 1 shows the 10 first-level categories of DOD’s work breakdown structure. For the full work breakdown structure, see appendix IV. Finally, the instruction requires the military services to provide a reason for all projected shortfalls, strategies to mitigate the effects of each projected shortfall, and actions taken by the services to rectify any projected workload or capability shortfall. A projected shortfall exists if a military service does not expect to have sufficient workload to sustain the required level of capability that has been identified. For example, an armed service may have identified 10,000 direct labor hours of core capability requirements for ground vehicles, but have only 4,000 hours of projected depot maintenance work for ground vehicles—resulting in a projected workload shortfall of 6,000 hours. In 2012 DOD submitted its first biennial core report to Congress, and we found that DOD did not provide sufficient explanations when reporting on the military services’ shortfalls in core capability requirements. In 2014 DOD submitted its second biennial core report to Congress, and we found that DOD did not have accurate and complete data in the report. In 2016 DOD submitted its third biennial core report to Congress, and we found (1) data errors; (2) inaccurate inter-service workload across the military services due to lack of coordination in reporting this information; (3) inconsistent calculations or display of workload shortfalls across the military services; and (4) inconsistent calculations of the estimated cost of planned workload across the military services. We made recommendations to address each issue. Further, we identified additional information that could increase the report’s transparency, and we suggested that Congress consider amending section 2464 to include additional elements to increase the transparency of future biennial core reports. Consistent with our recommendations, Congress amended section 2464 and added additional reporting requirements. We discuss DOD’s actions to address our specific recommendations to improve the completeness of its 2018 Biennial Core Report later in this report. In the 2018 Biennial Core Report, DOD and the military services addressed 8 of 10 required reporting elements, as shown in table 1 and discussed in more detail below. According to department officials, the department did not address two of the elements because changes to its guidance and processes for developing the 2018 report resulted in the 2016 and 2018 reports not being directly comparable. DOD officials stated that they plan to address these two elements in the 2020 Biennial Core Report. To address reporting elements 1 and 2, the military services presented their respective requirements and projected workloads in direct labor hours and associated costs, using the work breakdown structure. Table 2 shows DOD’s reported direct labor hours for the depots’ core requirements, as well as projected maintenance workloads and costs of workloads to sustain core requirements by military service. The military services presented core requirements and workloads, down to the second-level subcategories, to address reporting element 7. This structure represents all of the sub-specialties required to maintain core depot-level capabilities across the 10 categories of the work breakdown structure. For example, the aircraft category is broken down into 7 second-level subcategories: rotary, vertical/short take-off and landing, cargo/tanker, fighter/attack, bomber, unmanned systems, and aircraft engines. The Army, Navy, and Air Force also identified the items they placed into the “Other” category to address reporting element 9. The Marine Corps did not place any core requirements in the “Other” category in the 2018 Biennial Core Report and therefore was not required to address this reporting element. Specifically: The Army identified requirements associated with items such as air conditioners, food service hygiene equipment, chemical defense equipment, and water purification; The Navy identified requirements associated with specialty aircraft and aircraft components that are common across multiple platforms; and The Air Force identified requirements associated with specialty items such as surveillance aircraft, missile components, and communications/electronic equipment that do not fall under other distinct work breakdown structure subcategories. The military services each identified projected shortfalls at the first- and second-levels of the work breakdown structure (elements 3 and 4), reasons for those shortfalls (element 3), and mitigation plans for the projected shortfalls (element 3). This includes—in some cases— leveraging excess core capabilities in one workload category to mitigate projected shortfalls in another category (elements 5 and 8). Specifically: Army: The Army reported a total projected shortfall of about 2.9 million direct labor hours, as shown in table 3. It identified projected shortfalls in 5 of the 10 first-level work breakdown structure categories, and in 13 of the 33 second-level categories. The Army identified a number of reasons for these projected shortfalls. Army officials stated that these reasons generally contributed to shortfalls across the various work breakdown categories. They also noted the challenge of calculating shortfalls based on comparing current workloads with predicted workloads that were based on potential future Army strategies. The Army identified the following specific reasons for shortfalls: DOD’s updated defense planning scenarios increased the Army’s equipment requirements. These additional requirements resulted in a greater total core depot requirement for the Army, which in turn contributed to projected shortfalls. The Army noted that DOD’s most recent Future Years Defense Program lacked sufficient depot maintenance funding (that is, money to pay for direct labor hours) to meet core capability requirements. The Army cited newly established software depot maintenance requirements as one of the reasons for its shortfall. Specifically, DOD updated requirements for reporting depot resources associated with upgrading and maintaining software in weapon systems. According to the Army’s 2018 core report submission, the Army previously determined this requirement based on the number of people assigned to the Army’s software sustainment activities. However, the Army revised its methodology for calculating its software sustainment workload to reflect actual workload, not just the number of people conducting the work. After identifying projected shortfalls, officials used that information to determine how best to close gaps and mitigate risks in future implementation. Specifically, the Army is currently working to move software-related direct labor hours from contractor to military sources, which will help the Army mitigate—that is, shrink—its projected shortfall by fiscal year 2020. The Army reported that it plans to mitigate many of its projected core shortfalls by using skill sets similar to those required for maintaining a core capability in repairing equipment for foreign militaries. Officials stated that the Army plans to hire and train maintenance personnel to conduct maintenance work associated with the foreign military sales program. This workload will also assist the Army in meeting its core capability requirements for Army systems, increasing the total projected workload, and decreasing estimated shortfalls. Additionally, the Army identified mitigations for specific shortfalls—for example, replacing old generators with a new system by fiscal year 2025 will mitigate its shortfall in support equipment. Navy: The Navy reported that it did not project an overall shortfall, nor did it project any shortfalls at the first- or second-level of the work breakdown structure, and therefore it did not provide mitigation plans. Navy and OSD officials noted that the Navy and the department differ regarding the definition of software sustainment. Specifically, a Navy official stated that the service views software sustainment as an engineering function, not a depot maintenance function. This official observed that while the Navy believes software sustainment to be critical to maintaining its weapon systems, it believes that managing software sustainment as depot maintenance is not the most effective approach for the Navy. As a result, the Navy did not report any software core capability requirement or projected workload for fiscal year 2019. OSD defined software maintenance and reporting requirements in its guidance requesting data from the military services for the biennial core report. In spite of differing perspectives between OSD and the Navy, OSD accepted the Navy’s core report submission, in which the Navy reported no core software maintenance capability requirements. Marine Corps: The Marine Corps reported that it did not project a total shortfall, but did project a shortfall of 82,971 direct labor hours in one second-level subcategory—that is, construction equipment—that falls in the ground vehicle first-level category. The Marine Corps identified a rationale and mitigation plan for its projected shortfall in construction equipment. The Marine Corps reported that general factors affecting maintenance workload and funding contributed to the shortfall, including: (1) After drawdowns from Iraq and Afghanistan, the Marine Corps repaired equipment to a desired level of combat effectiveness in line with current mission requirements and available resources. This led to fewer current maintenance needs and therefore reduced core maintenance workloads, creating projected shortfalls in some skill sets; and (2) The Marine Corps made changes to its force structure, which led to having more equipment in inventory, less equipment in use, and therefore less required maintenance. This created a shortfall in the skill set for construction equipment. To address this shortfall, the Marine Corps plans to use the excess workload in amphibious vehicles to mitigate the projected shortfall in construction equipment. Marine Corps officials stated that these second-level subcategories involve similar, tracked vehicles, which can be maintained using the same skill set. Air Force: The Air Force reported that it did not project a total shortfall, but did project shortfalls within the work breakdown structure, as shown in table 4. The Air Force identified projected overall shortfalls in 1 of the 10 first-level work breakdown structure categories, and in 7 of the 33 second-level work breakdown structure categories. The Air Force identified reasons and provided detailed explanations, as well as mitigation plans, for each projected shortfall. For example, it projected a shortfall in rotary workload according to Air Force officials because of staffing and supply issues with HH-60 Pave Hawk maintenance at Corpus Christi Army Depot. According to these officials, these maintenance issues have resulted in the Air Force’s using more contracted depot maintenance work on the HH-60 Pave Hawk in order to meet demand. As a result of the more extensive contracting of maintenance, planned workload at Corpus Christi Army Depot has been reduced, thereby creating a projected shortfall. The Air Force, Army, and Navy formed a team to address this projected shortfall. Air Force officials stated that contracts are being reduced and that they expect to resolve the maintenance issues before the 2020 Biennial Core Report. To address its projected shortfall in tactical missiles, the Air Force plans to identify Letterkenny Army Depot as the Technology Repair Center for this requirement, as the workloads are small in volume and the Letterkenny Army Depot can meet this requirement. In addition, the Air Force projected an overage of about 176,000 direct labor hours in strategic missiles. The Air Force believes that its projected workload in strategic missiles will allow it to maintain capability to repair tactical missiles—an area in which it projects a shortfall of about 42,000 direct labor hours. According to Air Force officials, the electronics on these two types of missiles are very similar and require the same skill set. DOD in the 2018 Biennial Core Report did not address progress made in implementing mitigation plans from the prior core report (element 6), nor did they address the degree to which projected workload reported in the prior core report was executed (element 10). According to Office of the Assistant Secretary of Defense for Logistics and Materiel Readiness (OASD L&MR) officials, they did not address these elements because the elements require DOD to compare information in the 2018 Biennial Core Report with information in the 2016 Biennial Core Report. Since DOD updated its guidance and processes for developing the 2018 Biennial Depot Core Report—in response to new statutory requirements and our prior recommendations—a meaningful comparison was not possible in the 2018 Biennial Core Report, according to OSD and military service officials. Additionally, DOD did not fully provide mitigation plans in its 2016 Biennial Core Report, as we reported in 2016. Therefore, DOD was unable to provide progress reports on 2016 mitigation plans. DOD officials told us that they plan to use the 2018 Biennial Core Report as a baseline for future biennial core reports, which will allow them to address elements 6 and 10. Specifically, they stated that they plan to provide progress reports on the mitigation plans they identified in the 2018 Biennial Core Report. Additionally, officials stated their intent to provide a comparison of the fiscal year 2019 projected workload reported in the 2018 Biennial Core Report with the actual workload for fiscal year 2019 contained in the 2020 Biennial Core Report. DOD’s 2018 Biennial Core Report is generally complete in that it lacks any obvious errors and aligns with supporting information provided by the military services. Specifically, unlike previous biennial core reports, data submissions provided to DOD by the military services are identical to the data in the 2018 Biennial Core Report, and there are no transposition errors. Further, based on our review of the services’ submissions to OSD, data and other information provided by the military services were accurately and appropriately included in DOD’s 2018 Biennial Core Report. Finally, our analysis of the report and the military services’ submissions did not identify errors in the summation of the data. DOD’s focused efforts in 2017 and 2018 to develop better guidance and procedures assisted in improving the completeness of DOD’s 2018 Biennial Core Report—in part, according to DOD officials, due to our prior recommendations. Specifically, in 2017 the OASD L&MR began drafting new guidance to identify required depot maintenance core capabilities and the associated workloads needed to sustain those capabilities. This guidance was finalized and issued by the Office of the Under Secretary of Defense for Acquisition and Sustainment in May 2018. Officials from OASD L&MR and the military services told us that they used the methodology in this new guidance to complete the 2018 Biennial Core Report in late 2017 and early 2018. Officials told us that our prior recommendations, based on our reviews of the 2012, 2014, and 2016 biennial core reports, served to guide DOD’s update of its guidance and procedures. The changes made by Congress to section 2464 were also incorporated into DOD’s new guidance to ensure compliance with the 10 reporting elements, as we previously discussed. During the course of our review, we found that DOD had addressed all of the recommendations from our prior reports on the 2012, 2014, and 2016 Biennial Core Reports. First, in our review of the 2012 Biennial Core Report, we found that DOD did not include explanations for each identified projected shortfall. We recommended that DOD include in its biennial core report to Congress detailed explanations for why the military services did not have the workloads to meet core maintenance requirements for each projected shortfall identified in the report. Officials with OASD L&MR said that the May 2018 updated version of DOD Instruction 4151.20 was revised to require the submission of a detailed rationale for any and all shortfalls, and a plan to either correct or mitigate the effects of the shortfalls. The instruction states further that the detailed rationale and plan will identify the reason for the shortfall; contain a strategy to mitigate the effects of the shortfall (for example, specific transferrable workload, transfer of private- sector workload); and include actions to rectify any capability or workload shortfalls, including a description of planned capital investment, timing, and planned workarounds until the new capabilities or workloads are available. DOD’s 2018 Biennial Core Report as previously discussed provided rationales for shortfalls. Second, in our review of the 2014 Biennial Core Report, we found that some data were incomplete. We recommended that DOD review its processes and implement needed improvements to help ensure accuracy and completeness. In response to this and our other prior recommendations, DOD updated DOD Instruction 4151.20 to include additional steps and more controls that ensure more complete and accurate data submissions. According to OSD officials, changes to the guidance included deleting data fields unrelated to core requirements; streamlining and clarifying reporting instructions; ensuring that service submissions be reviewed and approved by general, flag, or senior executive service officials; determining the weapon systems or other platforms that are in the Chairman of the Joint Chiefs of Staff strategic and contingency plans; addressing inter-service workloads; having the worksheet automatically calculate shortfalls; and defining “software” and “software maintenance.” Most recently, in our review of the 2016 Biennial Core Report, we found (1) data errors; (2) inconsistent capture of inter-service workloads across the military services; (3) inconsistent calculations or transpositions of projected workload shortfalls across the military services; and (4) inconsistent calculations of the estimated cost of projected workloads across the military services. We recommended that DOD update its guidance—in particular DOD Instruction 4151.20—to require future biennial core reports to include instructions to the reporting agencies on how to (1) report additional depot workloads performed that have not been identified as core requirements; (2) accurately capture inter-service workloads; (3) calculate projected shortfalls; and (4) estimate the cost of projected workloads. DOD took steps to address each of these issues. Specifically, DOD did the following: Issued guidance stating that the total adjusted core capability requirements and the total projected public-sector depot maintenance workloads both reflect core workloads, as well as workloads that have not been identified as sustaining core. Developed and provided to each of the military services a worksheet on which to submit their projected inter-service workloads. OSD also held a meeting with all of the military services to resolve any discrepancies between their respective submissions. Created worksheets with formulas to automatically calculate the projected shortfalls at the subcategory level of the work breakdown structure for each service. Issued updated guidance to indicate that the estimated costs of the projected workloads to sustain the core capability requirements were to be included. According to OSD officials, these estimates are developed in accordance with financial management regulations and then applied to the estimated core sustaining workloads for each work breakdown structure, thereby providing a common baseline and process. In meetings with OSD and the military services, officials offered ideas for possible changes in future reports, such as including additional information on inter-service workloads to increase congressional visibility regarding coordination on depot maintenance across the military services. Additionally, OSD officials noted that they were considering the inclusion of additional information in future reports on how costs of projected workloads are calculated. Information on this is provided in DOD Instruction 4151.20, but not in its biennial core report. According to OSD officials, the department plans to consider these and other proposed changes from the military services and other stakeholders to its biennial core reporting process and supporting guidance. Given that DOD has made considerable progress by improving both the completeness of the 2018 Biennial Core Report and its guidance on the development of the report, we are not making recommendations at this time. We provided a draft of this report to DOD for comment. DOD provided technical comments, which we included as appropriate. We are sending copies of this report to appropriate congressional committees, the Secretary of Defense, and the Secretaries of the Military Departments. 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 Diana Maurer at (202) 512-9627 or maurerd@gao.gov. Contact points for our Office of Congressional Relations and Public Affairs may be found on the last page of this report. GAO staff who made key contributions to this report are listed in appendix V. Appendix I: Complete Text of 10 U.S.C. § 2464(d) (d) Biennial core report. Not later than April 1 of each even-numbered year, the Secretary of Defense shall submit to Congress a report identifying, for each of the armed forces (except for the Coast Guard), for the fiscal year after the fiscal year during which the report is submitted, each of the following: 1. The core depot-level maintenance and repair capability requirements and sustaining workloads, organized by work breakdown structure, expressed in direct labor hours. 2. The corresponding workloads necessary to sustain core depot-level maintenance and repair capability requirements, expressed in direct labor hours and cost. 3. In any case where core depot-level maintenance and repair capability requirements exceed or are expected to exceed sustaining workloads, a detailed rationale for any and all shortfalls and a plan either to correct or mitigate the effects of the shortfalls. 4. Any workload shortfalls at any work breakdown structure category designated as a lower-level category pursuant to Department of Defense Instruction 4151.20, or any successor instruction. 5. A description of any workload executed at a category designated as a first-level category pursuant to such Instruction, or any successor instruction, that could be used to mitigate shortfalls in similar categories. 6. A description of any progress made on implementing mitigation plans developed pursuant to paragraph (3). 7. A description of core capability requirements and corresponding workloads at the first level category. 8. In the case of any shortfall that is identified, a description of the shortfall and an identification of the subcategory of the work breakdown structure in which the shortfall occurred. 9. In the case of any work breakdown structure category designated as a special interest item or other pursuant to such Instruction, or any successor instruction, an explanation for such designation. 10. Whether the core depot-level maintenance and repair capability requirements described in the report submitted under this subsection for the preceding fiscal year have been executed. In 1984 Congress passed legislation limiting the private contracting of certain core logistics functions. This law required the Department of Defense (DOD) to maintain a logistics capability to ensure a ready and controlled source of technical competence and resources. In 1988 Congress codified this law, as amended, at section 2464 of title 10 of the U.S. Code. While section 2464 has been amended multiple times since then, the requirement for DOD to maintain a core logistics capability that is government-owned and government-operated has persisted. In 2011 Congress added a requirement for DOD to provide a biennial core report. Most recently, in fiscal year 2018 Congress added additional elements that DOD is required to address in its biennial core reports. Among other things, changes to the statute are illustrated in figure 2 below. Section 2464(d) of Title 10 of the United States Code requires the Department of Defense (DOD), among other things, to submit to Congress a biennial report providing information on its core depot-level maintenance and repair capability requirements and workload. Specifically, section 2464(d) identifies 10 elements that DOD must address for each of the armed services (except for the Coast Guard) in its biennial report concerning depot-maintenance requirements and workload. Section 2464 also requires us to review DOD’s report for compliance with section 2464 and assess the completeness of the report. DOD submitted its most recent biennial core report to Congress on May 23, 2018. To determine the extent to which the DOD 2018 Biennial Core Report complies with section 2464(d), we analyzed the text of the report and obtained supporting information on DOD’s process to determine its core maintenance capability for fiscal year 2019. Two GAO analysts independently reviewed DOD’s report to determine the extent to which it addressed each element required by the statute. All initial disagreements between the two GAO analysts were discussed and resolved through consensus. For the military services, when the report explicitly included all parts of the required reporting element, we determined that DOD “addressed” the element. When the report did not explicitly include any part of the element, we determined that DOD “did not address” the element. If the report included some aspects of an element, but not all, then we determined that DOD “partially addressed” the element. We compared the types of information and data provided by each of the military services with the data that the Office of the Secretary of Defense (OSD) included in the 2018 Biennial Core Report, to assess consistency. We also discussed our preliminary analyses with OSD and military service officials to gain additional insight into their analysis and efforts to address the statutory requirements. To assess the report’s completeness, we obtained and analyzed the fiscal year 2019 data used in compiling DOD’s 2018 Biennial Core Report, including core capability requirements and projected sustaining workload expressed in direct labor hours and cost and other information, such as workload shortfall explanations. We compared the reporting agencies’ submissions with the reporting template in DOD Instruction 4151.20 in order to determine the extent to which the reporting agencies submitted the information required by DOD’s instruction, and we identified any inconsistencies or errors. In order to determine whether these data and information were complete, we performed a number of data check steps to identify transposition inconsistencies or errors, and we discussed our analyses with OSD and military service officials. These steps included (1) reviewing each military service’s submission to verify that it had consistently calculated and reported the direct labor hours identified as the total adjusted requirements and the workload needed to sustain depot maintenance core capability requirements; and (2) reconciling the information in the report against each military service’s submission, for accuracy. However, as in the past reviews of DOD’s biennial core reports, we did not assess the reliability of the underlying data provided by the military services for the 2018 DOD Biennial Core Report. The team also met with OSD and reporting agency officials responsible for overseeing the data collection and preparing the data submissions, to obtain clarification and understanding of the content of the submissions, as well as to discuss the department’s guidance and processes used to collect the data for the report. Lastly, we reviewed DOD’s actions to address our prior recommendations that were targeted at improving the completeness of DOD’s biennial report. We conducted this performance audit from May 2018 to November 2018 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. Appendix IV: Category Levels from the Department of Defense’s (DOD) Depot Maintenance Core Capability Worksheet Work Breakdown Structure Category 1. Aircraft 1.2 Vertical/Short Takeoff and Landing 2. Diana Maurer, (202) 512-9627 or maurerd@gao.gov. In addition to the named contact above, John Bumgarner, Assistant Director; Thomas Gosling, Assistant Director; Pat Donahue, Amie Lesser, Shahrzad Nikoo, Bethann E. Ritter Snyder, Walter Vance, Cheryl Weissman, and Melissa Wohlgemuth contributed to this report.

Summary: DOD uses both military depots and contractors to maintain its complex weapon systems and equipment. Recognizing the depots' key role and the risk of overreliance on contractors, section 2464 of title 10 of the U.S. Code requires DOD to maintain a core logistics capability that is government-owned and operated, involving a combination of personnel, facilities, equipment, processes, and technology. Section 2464 requires DOD to provide a Biennial Core Report to Congress that addresses 10 reporting elements, including information on its core capability requirements and projected workload for the next fiscal year. Section 2464 includes a provision that GAO review DOD's Biennial Core Reports for compliance and completeness. In reviewing the 2018 Biennial Core Report, GAO assessed the extent to which DOD's report (1) addressed the 10 reporting elements required by section 2464(d), and (2) is complete. GAO reviewed and analyzed relevant legislation, DOD guidance, and the 2018 Biennial Core Report, and met with DOD and military service officials to discuss the processes used to develop the information in DOD's 2018 Biennial Core Report. In its 2018 Biennial Core Report, the Department of Defense (DOD) addressed 8 of 10 reporting elements. Specifically, DOD reported, by military service, its: depot maintenance workload required to sustain core maintenance capability requirements, based on contingency planning scenarios; projected fiscal year 2019 depot maintenance workloads; and projected fiscal year 2019 shortfalls (i.e., insufficient workload to sustain the required level of capability) and rationales and mitigations for those shortfalls. The Army reported a projected workload for fiscal year 2019 that would meet about 84 percent of its identified core capability—a shortfall of 2.9 million direct labor hours (see figure). The Army identified numerous reasons—such as newly established software depot maintenance requirements—for its shortfalls. Furthermore, the Army presented mitigation plans for its shortfalls, such as moving software-related work from contractor to military sources. The other services did not report overall shortfalls, but some services reported shortfalls associated with specific types of work. For example, the Air Force reported a shortage associated with the repair of tactical missiles. As a mitigation plan, the Air Force stated that it plans to use workload associated with repairing strategic missiles to maintain this capability, since the electronics on the two types of missiles are very similar and require the same maintenance skill set. DOD did not address two required reporting elements—progress in implementing mitigation plans from the 2016 biennial core report, and the degree to which projected workload reported in the 2016 biennial core report was executed. According to DOD officials, changes in its guidance and processes for developing the 2018 report resulted in the 2016 and 2018 reports not being directly comparable. However, DOD officials stated that they plan to address these two elements in the 2020 Biennial Core Report. DOD's 2018 Biennial Core Report is generally complete, in that it lacks obvious errors and aligns with supporting information provided by the services. DOD's concerted efforts to implement better guidance and procedures—in part, according to DOD officials, by implementing GAO's prior recommendations from 2012, 2014, and 2016—assisted in improving the completeness of the report.