Maritime Signal Flags

A visual alphabet that is still mandatory at sea

The International Code of Signals (ICS, also called INTERCO) is the maritime flag system maintained by the International Maritime Organization (IMO) for visual communication between vessels regardless of the crews' spoken language. It defines 26 rectangular flags (swallow-tailed for Alfa and Bravo) for the letters A-Z and 10 triangular pennants for the digits 0-9, each with its own colors and geometric pattern, stripes, quarters, crosses, diagonals, designed to stay legible at a distance, even in poor light. When flown alone, each letter flag carries a standardized, universally recognized emergency or maneuvering meaning, Oscar alone means 'man overboard', Whiskey alone means 'I require medical assistance'. The 10 numeral pennants, by contrast, have no individual meaning: they only represent a digit within a larger signal, such as a bearing, date or time. Combining two or more flags forms thousands of additional coded signals, a separate universe outside this tool's scope, which covers only the meaning of each flag flown by itself.

Browse the chart or spell out your own text

1. In the reference chart, search by letter, digit or a word from the meaning, or filter to letters only or numerals only.
2. Click a flag in the list to see its full colored design and official meaning up close (or the explanation, when a flag has no standalone meaning).
3. Switch to 'Spell with flags', type any text and watch the flag sequence build, spaces and punctuation with no matching flag show up as a small gap marker.

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Sources and references for this tool

These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.

• International maritime signal flagsWikipedia, Flag chart and meanings verified against the International Code of Signals.
• Annex IV: International Distress SignalsUS Coast Guard Navigation Center, Official source for the international distress signal (November + Charlie).
• International Code of Signals (Overview)Flags Of The World (crwflags.com), Vexillology reference used to confirm each flag's shape and design.

Frequently asked questions

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