GPS Alternatives: DOD is Developing Navigation Systems but is Not Measuring Overall Progress, Report to the Committee on Armed Services, U.S. Senate [open pdf - 4MB]
From the Highlights: "DOD primarily relies on GPS [Global Positioning System] for accurate PNT [position, navigation, and timing] data, which is essential to effective military operations. However, multiple threats can render GPS data unavailable or inaccurate. DOD recognizes the threats to GPS and is taking steps to address them by developing more robust GPS capabilities and alternative PNT technologies. GAO [Government Accountability Office] was asked to review DOD's acquisition of alternative PNT technologies. This report discusses (1) the threats facing GPS; (2) DOD's alternative PNT efforts and their business cases; and (3) DOD's oversight of its PNT portfolio. This is a public version of a sensitive report that GAO issued in April 2022. Information that DOD deemed to be sensitive has been omitted."
Government Accountability Office: https://www.gao.gov/