Maritime signal flags form the International Code of Signals (ICS), a system that lets vessels of any nationality exchange safety and navigation messages without a shared spoken language. Each letter of the alphabet has a uniquely coloured flag with its own name and a defined meaning when flown alone. This encoder spells any text using those flag names and shows each flag’s standalone significance.
How it works
The ICS assigns 26 alphabet flags, named Alfa, Bravo, Charlie, …, Zulu (note Alfa and Juliett are spelled to match the NATO alphabet). When encoding, the tool maps each letter to its flag name and appends a short note of the flag’s single-flag meaning, such as A — Alfa (Diver down; keep clear).
Spaces separate words, and any digit is labelled as a numeral pennant because ICS sends numbers with dedicated pennants rather than letter flags. The output is a plain-text list, one labelled line per character.
Example
Spelling SOS produces three lines: S — Sierra (My engines are going astern), O — Oscar (Man overboard), S — Sierra (...). Hoisting Oscar alone is itself the recognised man-overboard signal, which is why these single-flag meanings matter at sea.
The 26 alphabet flags and their single-flag meanings
Each ICS flag has a distinct colour and geometric pattern chosen to be identifiable at sea distance, where finer details blur. Single-flag signals cover the most time-critical safety and operational situations:
| Flag | Name | Single-flag meaning |
|---|---|---|
| A | Alfa | Diver down; keep well clear at slow speed |
| B | Bravo | Dangerous cargo |
| C | Charlie | Yes / Affirmative |
| D | Delta | Keep clear; I am manoeuvring with difficulty |
| E | Echo | Altering course to starboard |
| F | Foxtrot | I am disabled; communicate with me |
| G | Golf | I require a pilot |
| H | Hotel | Pilot on board |
| I | India | Altering course to port |
| J | Juliett | On fire; dangerous cargo; keep well clear |
| K | Kilo | I wish to communicate with you |
| L | Lima | You should stop your vessel instantly |
| M | Mike | My vessel is stopped; making no way |
| N | November | No / Negative |
| O | Oscar | Man overboard |
| P | Papa | Vessel about to sail (in harbour); nets fouled (fishing) |
| Q | Quebec | My vessel is healthy; request clearance |
| R | Romeo | (No single-flag meaning in current ICS) |
| S | Sierra | My engines are going full speed astern |
| T | Tango | Keep clear; engaged in pair trawling |
| U | Uniform | You are running into danger |
| V | Victor | I require assistance |
| W | Whiskey | I require medical assistance |
| X | X-ray | Stop your intention; watch for my signals |
| Y | Yankee | I am dragging anchor |
| Z | Zulu | I require a tug |
Using flag signals in practice
Modern vessels use VHF radio for most ship-to-ship communication, but flag signals remain the universal non-electronic fallback and are required display items for certain situations — a vessel with a diver below must fly Alfa, regardless of other communications available.
Multi-flag hoists convey specific messages from the ICS codebook. For example, the two-flag combination NC is the recognized distress signal when hoisted from a vessel. The ICS codebook, published by the International Maritime Organization, covers over 300 signal combinations for navigational, medical, meteorological, and operational messages.
This encoder produces the letter names in the Alfa–Zulu convention, which is also identical to the NATO phonetic alphabet for letters A through Z. Both systems use the same names for all 26 flags and phonetic letters, making this tool equally useful for anyone working across maritime and NATO contexts.