Coastal blackouts concealed targets and exposed signals

When were coastal blackouts first used, and did they affect navigation aids?

They were considered from the Napoleonic era onward, and wartime blackouts could extinguish lights and remove buoys as well as conceal the coast.

Organized concern with coastal blackouts dates to the Napoleonic period. Darkening settlements made it harder for hostile ships to identify individual buildings and aim against the shore. It also created a controlled background in which a lamp used to signal smugglers, spies, or a waiting vessel would stand out. Navigation suffered because lights, buoys, and other aids might be extinguished or removed during wartime. The policy traded routine maritime safety for concealment, counterintelligence, and coastal defense.