A GAO performance audit found that DOD's military services measure and report facility utilization inconsistently, undermining the department's ability to identify genuinely underused real property. Because DOD has not held the services accountable for following its own utilization guidance, unreliable data continues to shape - or fail to shape - facility decisions. Compounding the problem, installations report making costly renovation, mothballing and demolition choices without any detailed guidance on how to weigh sustainment, use and disposal risk: historic buildings must be kept in usable condition even when vacant, and demolition of unneeded facilities lags for want of dedicated funding. GAO is making five recommendations to close these data and guidance gaps; DOD generally concurred. DOD's real property includes land and three types of facilities - buildings, structures and linear structures such as roads and fences - and has been on GAO's High-Risk List for federal real property management since 2003. Each military service maintains its own inventory system feeding into DOD's enterprise Real Property Asset Database (RPAD), and each is required by DOD Instruction 4165.70 and by supplementary 2016 utilization guidance to periodically review its holdings, calculate a standardized utilization rate, and identify and report unneeded or underused facilities. For this review, covering June 2022 to March 2025, GAO assessed DOD and service guidance, analyzed RPAD and service data, and examined a non-generalizable sample of 19 installations selected for their excess, surplus or low-utilization data, visiting eight of them and interviewing officials at all 19. Over 700,000 DOD facilities with a combined replacement value of about $2.2 trillion, as of fiscal year 2023. $181.1 billion deferred-maintenance backlog, against average annual spending of $14.6 billion on new construction and $15.3 billion on maintenance and repair. 2,283 facilities reported excess and 2,170 disposed of, across all services, in fiscal year 2022. Non-generalizable sample of 19 installations reviewed, 8 visited in person, selected based on excess, surplus and low-utilization data. DOD Instruction 4165.70 and a 2016 ASD (EI&E) memorandum require standardized measurement and reporting of facility utilization rates by asset type and operational status. Military departments must maintain current, validated real property inventories, with physical inventories every 5 years (3 years for historic assets). Military services must notify other DOD components of unneeded property before proceeding to dispose of it. The Air Force did not fully implement the 2016 utilization-reporting methodology until December 2020, two years after DOD's August 2018 deadline. DOD funded only about 80 percent of its facility sustainment requirements against its own 90 percent target, contributing to the $181.1 billion deferred-maintenance backlog. Services have piloted space-utilization tools (the Army's RPSA/ePRISMS, the Navy's Shore Facilities Planning System and Facility Investment Model) and "demolition banks" that offset new construction with disposal of similar square footage elsewhere. Installations increasingly rely on relocatable facilities such as trailers to meet unexpected space needs, but several ended up funding long-term maintenance for what were meant to be temporary structures. Utilization data are inconsistent and, in cases GAO observed on-site (e.g. a headquarters building showing 28% utilization that appeared nearly fully occupied), inaccurate, undermining DOD and congressional decision-making. Without risk-management guidance, installations cannot resolve competing sustainment/demolition priorities: Fort Bliss could not fund the $14 million disposal of an old hospital, and the Navy's demolition backlog is estimated at $700 million. "The Navy and Marine Corps calculate an average utilization rate across a set of similar facilities rather than calculate utilization of individual facilities... Army officials stated the service directly inputs facility utilization rates into its real property information system. However, we found since fiscal year 2020 that the Army has not reported any underutilized property in active operational status. For example, in the fiscal year 2022 RPAD data, the Army reported 5,521 underutilized facilities, all of which showed 0-percent utilization." (GAO-25-106132, p. 10) "military service officials said that they are aware they are not following ASD (EI&E) guidance and that they expect utilization data are inaccurate. Since ensuring the accuracy of utilization rates is not a priority, DOD has not held them accountable for following its guidance and improving data quality." (GAO-25-106132, p. 11) "installation officials told us that they are limited in their ability to optimize their facilities because the military services have not issued detailed guidance specifying how they should assess and manage risks associated with their real property inventory, including determining how to weigh competing priorities relating to sustainment, use, and disposal of property." (GAO-25-106132, p. 23) "officials at Fort Bliss explained that they have some historic buildings that are not in use because of their poor condition and age. However, they noted that Fort Bliss is still required to do certain types of maintenance on these buildings, such as replacement of their roofs." (GAO-25-106132, p. 17-18) "a building at Joint Base Lewis-McChord was declared excess in 2017 and was placed on the demolition list... the building was still in place during our visit... Navy headquarters officials... estimated the Navy's backlog of demolition projects would cost about $700 million to address; about $229 million was funded in fiscal year 2024 and $170 million in fiscal year 2025." (GAO-25-106132, p. 19-22)