Maritime Signal Flag Lookup

About this calculator

The International Code of Signals assigns each letter of the alphabet its own distinctively colored and patterned flag, so that ships can communicate short standardized messages visually across open water without a shared spoken language. A single flag flown alone carries a specific urgent meaning — for example, “A” (Alfa) means “I have a diver down; keep well clear at slow speed,” while “O” (Oscar) means “Man overboard.” This tool looks up the ICS meaning and NATO phonetic name for any single letter from A to Z.

Signal flags remain part of standard training for merchant mariners, naval personnel, sailing racers and maritime cadets, who must recognize single-letter flags on sight for safety-critical situations and use flag hoists combined with the phonetic alphabet in radio communication. They're also flown ceremonially and used in yacht racing to signal course changes, postponements and other race-committee instructions.