International maritime signal flags

The system of international maritime signal flags is a way of representing individual letters of the alphabet in signals to or from ships. It is a component of the International Code of Signals. ^[1]

There are various methods that the flags can be used as signals:

each flag spells out a letter of an alphabetic message.
individual flags have specific and standard meanings; for example, diving support vessels raise the "A flag" indicating their inability to move from their current ___location because they have a diver underwater.
one or more flags form a code word whose meaning can be looked up in a code book held by both parties. An example is the Popham numeric code used at the Battle of Trafalgar.
in yacht racing and dinghy racing, flags have other meanings; for example, the P flag is used as the "preparatory" flag to indicate an imminent start, and the S flag means "shortened course".

NATO uses an extra set of flags to communicate specific types of messages.

Letters

A	Alfa	I have a diver down; keep well clear at slow speed
B	Bravo	I am taking in, or discharging, or carrying dangerous goods. (Originally used by the Royal Navy specifically for military explosives.)
C	Charlie	Yes. ^[1]
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. When made by fishing vessels operating in close proximity on the fishing grounds it means: "I am hauling nets".
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, or I am leaking dangerous cargo.
K	Kilo	I wish to communicate with you.
L	Lima	You should stop your vessel instantly.
M	Mike	My vessel is stopped and making no way through the water.
N	November	No. ^[2]
O	Oscar	Man overboard (often attached to the man overboard pole on boats).
P	Papa	The Blue Peter. In harbor — All persons should report on board as the vessel is about to proceed to sea. At sea — It may be used by fishing vessels to mean: "My nets have come fast upon an obstruction".
Q	Quebec	My vessel is "healthy" and I request free pratique.
R	Romeo	No meaning in the flag code.
S	Sierra	I am operating astern propulsion.
T	Tango	Keep clear of me; I am engaged in pair trawling.
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. When made by fishing vessels operating in close proximity on the fishing grounds it means: "I am shooting nets".

* ^ N and C together (No and Yes) is used as a distress signal.

Numbers

Type of flag	0	1	2	3	4	5	6	7	8	9
NATO flags
Pennants

Other flags


Prompt	First substitute	Second substitute	Third substitute	Fourth substitute
NATO signals

Code/answer (ANS)	Preparation (PREP)	Question (INT)	Negation (NEGAT)	Designation (DESIG)

Alter course (CORPEN)	Turn (TURN)	Screen (SCREEN)	Speed (SPEED)	Station (STATION)

Port (PORT)	Starboard (STBD)	Formation (FORM)	Division (DIV)	Squadron (SQUAD)

Group (FLOT)	Subdivision (SUBDIV)	Emergency (EMERG)