In EW planning, which navigation aids provide redundancy when GPS is denied or degraded?

• A. Inertial navigation, VOR/ILS, and TERCOM can provide redundancy when GPS is denied or degraded.
• B. They are primarily used for weather updates.
• C. They are used only for time synchronization.
• D. They are irrelevant to EW.

Answer: (A)

The key idea is having multiple independent ways to determine position and navigation when GPS is unavailable. Inertial navigation relies on internal sensors (accelerometers and gyros) to track movement and orientation, giving immediate, GPS-free position data. It’s self-contained, but it drifts over time, so it’s most reliable when used with other updates to correct the error.

VOR/ILS provide ground-based radio navigation cues. VOR gives a bearing to a known station, and ILS offers precise localizer and glide-slope signals for approach guidance. These are independent of GPS, though they require radio reception and line-of-sight to the stations, which can be limited by terrain or jamming, yet they still serve as solid redundancy.

TERCOM, or terrain-contour matching, uses terrain information and radar or imaging data to match against a stored map and estimate your position and altitude. This method doesn’t depend on satellite signals, so it remains functional in GPS-denied conditions, though its accuracy depends on terrain features and sensor quality.

Together, these systems provide redundancy by offering alternative, independent reference points for navigation when GPS is degraded, enhancing situational awareness and EW planning resilience.

The other options describe activities unrelated to navigation aids for EW planning (weather updates, time synchronization) or claim irrelevance, which doesn’t align with how navigation robustness is maintained in GPS-denied environments.