What Do the Flags Mean

Signal flags are used to identify ships and were also to communicate between ships in the era before radio. The first International Code was drafted in 1855. It contained 70,000 signals using 18 flags! The International Code of Signals, as it is known today, has gone through several revisions since then.

Even today, because these flags have a specific, internationally agreed upon meaning, some signal flags are used by ships to communicate. For example, the "B" flag, or "Bravo" flag, is understood to mean that the ship flying that flag is carrying dangerous cargo. Additionally, flags can be combined in groups of two, three, four, five, and even six and seven flag groups.

There are 26 square flags for the letters of the English alphabet, ten numerical pendants, one answering pendant, and three "substitute" or "repeater" flags.

Only certain colors are used in signal flags, because these colors can be readily discerned over long distances at sea.

The 26 letter flags and their meanings are:

 Letter   Phonetic   Meaning   Flag 
 A  Alpha  I have a Diver down. Keep well clear at slow speed  International Maritime Flag for the letter A
 B  Bravo  I am taking on, carrying, or discharging dangerous cargo  International Maritime Flag for the letter b
 C  Charlie  Yes  International Maritime Flag for the letter c
 D  Delta  Keep clear of me; I am maneuvering with difficulty.  International Maritime Flag for the letter d
 E  Echo  I am altering my course to starboard  International Maritime Flag for the letter e
 F  Foxtrot  I am disabled; Communicate with me.  International Maritime Flag for the letter f
 G  Golf  I require a pilot.
 When made by fishing vessels on fishing grounds it means "I am hauling nets".
 International Maritime Flag for the letter g
 H  Hotel  I have a pilot on board.  International Maritime Flag for the letter h
 I  India  I am altering my course to port.  International Maritime Flag for the letter i
 J  Juliette  I am on fire and have dangerous cargo on board. Keep well clear of me. 
 (or "I am leaking dangerous cargo.") 
 International Maritime Flag for the letter j
 K  Kilo  I wish to communicate with you.  International Maritime Flag for the letter k
 L  Lima  You should stop your vessel immediately.  International Maritime Flag for the letter l
 M  Mike  My vessel is stopped and making no way through the water.  International Maritime Flag for the letter m
 N  November   No  International Maritime Flag for the letter n
 O  Oscar  Man Overboard  International Maritime Flag for the letter o
 P  Papa  At Sea - My nets have come fast upon an obstruction.
 In Port - All persons should report on board as the vessels is about to proceed to sea.  
 International Maritime Flag for the letter
 Q  Quebec  My vessel is healthy and I request free pratique  International Maritime Flag for the letter q
 R  Romeo  None  International Maritime Flag for the letter r
 S  Sierra  I am operating astern propulsion  International Maritime Flag for the letter s
 T  Tango  Keep clear of me. I am engaged in pair trawling.  International Maritime Flag for the letter T
 U  Uniform  You are running into danger.  International Maritime Flag for the letter U
 V  Victor  None  International Maritime Flag for the letter V
 W  Whiskey  I require medical assistance.  International Maritime Flag for the letter w
 X  X-Ray  Stop carrying out your intentions and watch for my signals.  International Maritime Flag for the letter x
 Y  Yankee  I am dragging my anchor.  International Maritime Flag for the letter y
 Z  Zulu  I require a tug.
 When made by fishing vessels on fishing grounds it means "I am shooting nets".
 International Maritime Flag for the letter z

Source: HO 102 - International Code of Signals, National Imagery and Mapping Agency, 1969 edition (Revised 2003)