Signal flags traded secrecy for usable command

Were signal flags too insecure for naval communication?

They were visible, but decoding them required observation and the right codebook, and fleets had few practical alternatives.

Signal flags were vulnerable to interception, but an enemy needed both a clear observation and an up-to-date codebook to understand them. Visibility alone did not reveal the coded meaning. Fleets had to weigh that risk against the lack of other practical ways to transmit orders at sea.