What system provides constant bearing and distance information using signals exchanged with surface beacons and aircraft?

The Tactical Air Navigation System (TACAN) is a vital navigational aid that allows aircraft to determine their position relative to a ground station or beacon. It works by exchanging signals with surface beacons, providing constant bearing and distance information. This system is particularly useful for military aviation, as it offers accurate navigation support in various operational environments.

TACAN uses a series of pulsed radio signals to establish these measurements, enabling pilots to ascertain their location with precision. This capability is crucial for missions that require exact navigation in both visual and instrument flight conditions.

On the other hand, GPS is a satellite-based system that provides absolute positioning rather than bearing and distance from a specific point. The Automatic Direction Finder (ADF) uses radio signals from AM stations for navigation and does not provide the same level of constant range information. Finally, VHF Navigation, specifically the Instrument Landing System (ILS), is primarily concerned with providing guidance during approaches to landing rather than continuous data on bearing and distance while in flight. Thus, TACAN stands out as the correct answer for providing constant bearing and distance information.