How wartime navies used lighthouses without guiding the enemy

Were lighthouses and other navigation aids kept operating during wartime?

Many lights were extinguished, but essential aids could be switched on briefly, retained in protected waters, or used selectively for navigation and deception.

Turning on a lighthouse for a known movement could help friendly ships but also reveal that traffic was passing, so its use had to be tightly controlled. Unlit buoys and aids inside estuaries or harbours could remain valuable where they offered little help to an enemy approaching from sea. Some lights or markers could also support deception by encouraging an opponent to infer the wrong route or activity. In the Thames Estuary, navigation marks around sunken explosives-laden ships protected wartime merchant traffic from a collision whose consequences no one wanted to test.