Each flag below is drawn to the International Code of Signals. A single flag hoisted on its own has a defined meaning; the same flags combined in a hoist spell messages letter by letter, and the flag names double as the NATO phonetic alphabet you use on the VHF.
The must-know flags
If you learn nothing else, learn these — their single-flag meanings are operational and you will see them flown for real.
I have a diver down; keep well clear at slow speed.
I am taking in, discharging, or carrying dangerous goods.
Yes (affirmative).
Keep clear of me; I am manoeuvring with difficulty.
No (negative).
Man overboard.
My vessel is healthy and I request free pratique.
I require assistance.
I require medical assistance.
The full alphabet
I am altering my course to starboard.
I am disabled; communicate with me.
I require a pilot. (Fishing vessels: I am hauling nets.)
I have a pilot on board.
I am altering my course to port.
I am on fire and have dangerous cargo on board; keep well clear of me.
I wish to communicate with you.
You should stop your vessel instantly.
My vessel is stopped and making no way through the water.
All persons report on board; the vessel is about to proceed to sea. (In harbour: the “Blue Peter”.)
No standard single-flag meaning (used in groups).
I am operating astern propulsion.
Keep clear of me; I am engaged in pair trawling.
You are running into danger.
Stop carrying out your intentions and watch for my signals.
I am dragging my anchor.
I require a tug. (Fishing vessels: I am shooting nets.)
Numerals & substitutes
Beyond the 26 letters there are ten numeral pennants (0–9), which are tapered pennants rather than rectangular flags so a number can never be mistaken for a letter, and three substitute (repeater) pennants used to repeat a flag already shown in the same hoist — so you can signal a double letter or digit without carrying two of the same flag.
Test yourself
The flag names are also the phonetic alphabet — pair this with the phonetic & procedure-words reference to lock both in at once.
Phonetic alphabet & procedure words →