Why did naval fleets use signal flags to control ships in battle?

In the context of naval warfare, signal flags were essential for maintaining command and control over fleets, particularly during the era of sail. Because ships were wind-constrained and moved slowly, they required a reliable method to coordinate formations and execute tactical maneuvers.1

Naval fleets utilized signal flags for the following reasons:

• Coordinated Control: Flags served as a primary means of transmitting prearranged messages, allowing commanders to direct the movements of multiple vessels within a formation.21
• Tactical Communication: During the age of sail, signal flags, along with lights or sail movements, provided a standardized way to communicate doctrine and tactical instructions across the fleet.21
• Historical Development: Over time, these systems became increasingly sophisticated. In the 16th century, codes were developed based on the number and position of flags. By the late 18th century, figures such as Admiral Richard Kempenfelt and Sir Home Popham refined these methods, significantly improving the effectiveness of ship-to-ship communication.2

While later eras introduced radio and other electronic means of communication, flag signaling remained a foundational element of naval tactical coordination for centuries.213