International Code of Signals (ICS)

A system of flags, codes, and symbols used by ships to communicate essential messages and ensure safety at sea, regardless of language barriers.

The International Code of Signals (ICS) is a globally recognised communication system designed to facilitate clear and unambiguous exchanges between vessels and between ships and shore stations. Established in the early 19th century and continually updated to meet modern maritime needs, the ICS employs a combination of signal flags, Morse code, radiotelephony, and written messages to convey information. Each flag in the system represents a letter of the alphabet, and combinations of these flags or codes correspond to specific messages, such as distress signals, navigational warnings, or medical emergencies. For example, the single-flag signal “A” indicates “I have a diver down; keep well clear at slow speed,” while “N” over “C” signals “I am in distress and require immediate assistance.”

The ICS is indispensable in situations where language differences might otherwise hinder communication. It is particularly vital in emergencies, where rapid and accurate information exchange can save lives and prevent accidents. The system is standardised by the International Maritime Organization (IMO), detailed in the ICS manual, and carried aboard most commercial vessels. While modern technologies like VHF radio and satellite communication have supplemented traditional signalling methods, the ICS remains a cornerstone of maritime safety, ensuring that vessels can communicate effectively in any circumstance.