TACAN (Tactical Air Navigation) is a military navigation system that provides aircraft with bearing and distance information to ground-based beacon stations, originally developed in the 1950s for U.S. military use. While technologically distinct from GNSS, TACAN represents an important component of the broader positioning, navigation, and timing (PNT) landscape and continues to provide backup navigation capability complementing satellite systems.

TACAN operates in the UHF frequency band (962-1213 MHz), providing two-way communication between aircraft and ground stations. The airborne interrogator transmits pulses that trigger responses from ground-based transponders. The aircraft receiver measures round-trip time to determine slant range (distance) to the station, while directional antenna patterns enable bearing determination. Combined range and bearing provide polar coordinates from the station, enabling point-to-point navigation along airways and approaches to TACAN-equipped airfields.

The system is closely related to the civilian VOR/DME (VHF Omnidirectional Range / Distance Measuring Equipment) system, and TACAN stations are often co-located with VOR facilities to create VORTAC installations that serve both military and civilian aircraft. TACAN provides higher accuracy than VOR and includes additional channels for military use, but operates on fundamentally similar principles of radio range and bearing measurement.

In the context of modern PNT infrastructure, TACAN serves as a backup navigation system when GNSS is unavailable due to jamming, spoofing, or system failures. Military operations in contested electromagnetic environments may require navigation without dependence on satellite systems, making ground-based aids like TACAN strategically important. While GNSS has become the primary positioning source for most aviation applications, diverse backup systems including TACAN, DME, and emerging technologies contribute to resilient navigation architectures that maintain capability across various threat scenarios.