RAF and Post Office lured German bombers with fake navigation beams

From 1940, German bombers navigated to British targets at night using Knickebein and related radio beam systems — ground beacons in occupied Europe transmitted directional beams a bomber's receiver could follow with precision, letting crews find targets in total darkness. Britain's obvious countermeasure, jamming those beacons outright, had a critical flaw: a jammed signal is instantly recognizable as jammed, alerting crews that something was wrong and prompting them to fall back on other navigation methods or abort the mission with suspicion intact.

Rather than block the German beams, British Post Office and RAF engineers under No. 80 Wing built 'Meacon' stations — masking beacon receivers that picked up the genuine German signal and rebroadcast it, unaltered, from a different British location on the same frequency. A bomber's receiver could not tell a rebroadcast beam from the real one; from the crew's perspective, their equipment was working exactly as expected.

Rebroadcast the genuine beam from a decoy location, so crews trust a signal that still works but points them off course by up to 100 miles.

Rebroadcasting the real signal made it indistinguishable from the original, so receivers saw no anomaly.

Crews' instruments appeared normal, giving no trigger to question the signal or switch methods.

Redirected trust kept the adversary acting on false info without realizing it was compromised.

The deception was more effective than jamming, which would have prompted suspicion and adaptation.

When blocking a channel would reveal interference, feed a convincing false version instead; if the target still trusts the source, you can redirect their decisions unnoticed.

German bombers were repeatedly drawn off course throughout the Blitz period, with documented cases including a Heinkel He 111 forced down into the sea near Bridport on Britain's south coast on 6 November 1940 after being lured off its intended track, and multiple other aircraft misled into flying toward or landing in British-controlled territory instead of their intended targets or return bases. Because crews' own instruments appeared to be functioning normally throughout, they had no way to detect the deception was occurring in real time.