How were flags and lights used for communication between early naval ships?

Early naval communication relied on prearranged systems to transmit information between vessels. By the 16th century, codes were developed that utilized the number and specific positioning of flags and lights to convey messages. In addition to these visual signals, the movement of a ship's sail or the number of cannon shots fired could also serve as signaling methods.1

During the 17th century, figures such as the British admiral Sir William Penn helped formalize these practices by developing regularized naval communication codes. These methods continued to evolve toward the end of the 18th century, when Admiral Richard Kempenfelt introduced a flag-signaling plan that laid the groundwork for modern systems, a process further refined by Sir Home Popham to improve the overall effectiveness of ship-to-ship communication.1