Abstract: To address the vulnerability of GNSS to interference and spoofing, as well as the insufficient resilience of a single positioning, navigation, and timing (PNT) system, and to meet the demand for high-reliability PNT services in critical industries, we investigated the backup support role and upgrade directions of Enhanced Long-Range Navigation (eLoran) within the national comprehensive PNT system. Taking the regional navigation anomaly event in Nanjing as a case study, we reviewed the technical principles and development status of eLoran. We analyzed its key bottlenecks from five aspects: signal structure, broadcasting capability, system architecture, device ecosystem, and management mechanisms. We proposed an upgrade pathway oriented toward “ubiquitous coverage, security and trustworthiness, and demand-driven services” and constructed an integrated backup standard. The results show that eLoran possesses advantages of high anti-interference capability, heterogeneous redundancy, and independent timing, enabling it to provide continuous and reliable backup PNT services when GNSS fails. Moreover, its integration with BeiDou and communication networks can form a multi-source collaborative spatiotemporal service system. We conclude that eLoran is a key technology for enhancing the security resilience of the national PNT system, and its systematic construction and industrialization are of significant strategic importance for building modern spatiotemporal infrastructure.