Editing Radio navigation (section)

===Beacons===
{{main|Electric beacon}}
The key to the transponder concept is that it can be used with existing radar systems. The [[List of World War II British naval radar#ASV II|ASV]] radar introduced by [[RAF Coastal Command]] was designed to track down submarines and ships by displaying the signal from two antennas side by side and allowing the operator to compare their relative strength. Adding a ground-based transponder immediately turned the same display into a system able to guide the aircraft towards a transponder, or "beacon" in this role, with high accuracy.{{fact|date=July 2022}}

The British put this concept to use in their [[Rebecca/Eureka transponding radar|Rebecca/Eureka]] system, where battery-powered "Eureka" transponders were triggered by airborne "Rebecca" radios and then displayed on ASV Mk. II radar sets. Eureka's were provided to French resistance fighters, who used them to call in supply drops with high accuracy. The US quickly adopted the system for paratroop operations, dropping the Eureka with pathfinder forces or partisans, and then homing in on those signals to mark the drop zones.{{fact|date=July 2022}}

The beacon system was widely used in the post-war era for blind bombing systems. Of particular note were systems used by the [[US Marines]] that allowed the signal to be delayed in such a way to offset the drop point. These systems allowed the troops at the front line to direct the aircraft to points in front of them, directing fire on the enemy. Beacons were widely used for temporary or mobile navigation as well, as the transponder systems were generally small and low-powered, able to be man portable or mounted on a [[Jeep]].{{fact|date=July 2022}}