Since the advent of humankind, communication has been fundamental to daily life, and with the rise of maritime navigation became even more fundamental in this more demanding task. Like human communication on land, naval communication was initially oral, often through relays in small boats. The first historical evidence of the use of sound and visual signals, such as flags or light signals, was recorded in the naval battle of Salamina, in 480 BC.
As a form of communication, these methods remained unchanged until the late Middle Ages, but the use of flags for ceremonial purposes became widespread from the thirteenth century on, indicating nationality, ownership of the ship or the fleet commander, uses often regulated by legislation, an example being the Aragonese ordinance of 1354, that defined which flags should be used and where to place them.
It is believed that the custom of covering the boats from stern to bow with cloths bearing the national or royal colors was introduced by the Portuguese, when sending the embassy of the Prior of the Hospital to the Queen of Sicily.
From the 16th century on, the European maritime expansion brought new challenges to navigation and communications, making it imperative to identify the vessels in a context of increasing competition and conflicts on the oceans, as well as increasingly larger fleets.
Navios de Guerra PortuguesesBiblioteca Central de Marinha
To standardize and facilitate communication between the ships of the fleets, the commanders began to draw up and distribute regiments that defined the use of sound signals such as cannon and musket shots and drums, daytime visual signals with flags, pennants, sails and banners.
In the second half of the 18th century, the Spanish introduced numeral flags into naval communications, which according to a previously established regiment, would transmit numbers that had a specific meaning through the combination of flags and pennants.
When visibility did not allow it, these numbers would be transmitted by sound signals such as artillery and musket shots and visual signals such as lights. This new system would also be implemented in the Portuguese Navy soon after and was already widespread in 1798.
In 1846, with the publication of the Commercial Code of Signals, for the use of the international merchant navy, resorted to the use of flags, pennants, balloons, and other means to transmit information through the combination of consonants of the alphabet, combined in pairs or groups of three and four, transmitted predetermined numbers, words, and phrases.
Throughout the 19th century, changes and additions were made to the various regiments in use, with no profound changes being observed in the methods of naval communication.
New flags were later added corresponding to new consonants, vowels and numerals, expanding the variety of information to be transmitted, forming the basis of the International Code of Signs (CIS) implemented in 1893, which is still in use today.
