Maritime Signal Flags
Authority: International Code of Signals (IMO, 2005 Edition)
The International Code of Signals assigns each letter flag a specific meaning when flown alone. Alfa means "diver down, keep clear"; Oscar means "man overboard"; Lima orders an immediate stop. Since a 1969 revision, flag Romeo carries no single-flag meaning and is used only as a numeral complement.
| Flag (Letter) | Code Word | Single-Flag Meaning |
|---|---|---|
| A | Alfa | I have a diver down; keep well clear at slow speed. |
| B | Bravo | I am taking in, discharging, or carrying dangerous goods. |
| C | Charlie | Affirmative. |
| D | Delta | Keep clear of me; I am maneuvering with difficulty. |
| E | Echo | I am altering my course to starboard. |
| F | Foxtrot | I am disabled; communicate with me. |
| G | Golf | I require a pilot. |
| H | Hotel | I have a pilot on board. |
| I | India | I am altering my course to port. |
| J | Juliett | I am on fire and have dangerous cargo on board: keep well clear of me. |
| K | Kilo | I wish to communicate with you. |
| L | Lima | Stop immediately. |
| M | Mike | My vessel is stopped and making no way through the water. |
| N | November | Negative. |
| O | Oscar | Man overboard. |
| P | Papa | (In harbor, the "Blue Peter") All persons should report on board; vessel is about to proceed to sea. |
| Q | Quebec | My vessel is healthy; I request free pratique. |
| R | Romeo | No single-flag meaning since the 1969 revision (formerly: "the way is off my ship"). |
| S | Sierra | I am operating astern propulsion. |
| T | Tango | Keep clear of me. |
| U | Uniform | You are running into danger. |
| V | Victor | I require assistance. |
| W | Whiskey | I require medical assistance. |
| X | Xray | Stop carrying out your intentions and watch for my signals. |
| Y | Yankee | I am dragging my anchor. |
| Z | Zulu | I require a tug. |
History & Origin
The modern International Code of Signals descends from the British Board of Trade's Commercial Code, first drafted in 1855 and published in 1857 with 18 flags capable of forming more than 70,000 signals. The system went international on January 1, 1901, and a major revision -- adopted at the 1932 Madrid International Radiotelegraph Conference and effective January 1, 1934 -- expanded the set to include square numeral flags for 0 through 9 and added dedicated aviation and medical vocabularies.
The current framework dates to a revision adopted in 1965 and effective in 1969 that deliberately narrowed the code's purpose: rather than spelling out long messages letter by letter, it refocused single- and two-flag hoists on safety of navigation, leaving longer coded messages to the code's vocabulary tables. That revision is also why flag Romeo, which previously carried its own single-flag meaning, was retired to numeral-complement duty only. The International Maritime Organization (IMO) now maintains the code, with its most recent edition published in 2005.
Reading the Flags
The full code comprises 40 flags: the 26 letter flags in the table above, 10 numeral pennants (0-9), three substitute (repeater) flags used when a signal needs to repeat a letter, and a single answering pennant a receiving vessel hoists to acknowledge a signal. Flown alone, each letter flag carries one of the code's most urgent or frequently needed messages -- Oscar for a man overboard, Lima ordering an immediate stop, Whiskey requesting medical assistance -- so it can be recognized and acted on at a distance without decoding a full hoist.
Combinations extend the vocabulary far beyond 26 meanings: the two-flag hoist November over Charlie is the code's standard distress signal, while three- and four-letter groups draw on the code's full vocabulary tables for everything from geographic positions to ship names.