Signaling

Knowledge of signal communications can be very valuable if radio equipment is inoperative, or there is no common frequency between you and the station you wish to communicate with, or where there is a language difference. Vessels within sight or hearing of each other may communicate using code flags, flashing lights, or sound signals.

The International Code of Signals

The International Code of Signals is published by the National Imagery and Mapping Agency as Publication No. 102. Pub. 102 contains signals that can be sent by flag hoists, flashing light and sound, and other means. The International Morse code is used for flashing light and sound signals, as well as radiotelegraphy. When you know these signals, try your hand at translations using semaphore, Morse code, or international code flags.

Semaphore	Morse Code	Code Flag	Code Flag Meaning
A	A	Alpha	Diver Down; Keep Clear
B	B	Bravo	Dangerous Cargo
C	C	Charlie	Yes
D	D	Delta	Keep Clear
E	E	Echo	Altering Course to Starboard
F	F	Foxtrot	Disabled
G	G	Golf	Want a Pilot
H	H	Hotel	Pilot on Board
I	I	India	Altering Course to Port
J	J	Juliet	On Fire; Keep Clear
K	K	Kilo	Desire to Communicate
L	L	Lima	Stop Instantly
M	M	Mike	I Am Stopped
N	N	November	No
O	O	Oscar	Man Overboard
P	P	Papa	About to Sail
Q	Q	Quebec	Request Pratique
R	R	Romeo
S	S	Sierra	Engines Going Astern
T	T	Tango	Keep Clear of Me
U	U	Uniform	Standing into Danger
V	V	Victor	Require Assistance
W	W	Whiskey	Require Medical Assistance
X	X	Xray	Stop Your Intention
Y	Y	Yankee	Am Dragging Anchor
Z	Z	Zulu	Require a Tug
0	0	0
1	1	1
2	2	2
3	3	3
4	4	4
5	5	5
6	6	6
7	7	7
8	8	8
9	9	9
Interval		Code
Attention		1st Substitute
numerals		2nd Substitute
alphabetic		3rd Substitute

Signals basically consist of single letters and two-letter combinations; three-letter combinations, all starting with "M," are used solely for medical messages. Many signals can be expanded or made more specific with complements. These may express a variation in the meaning of the basic signal; questions and answers related to the meaning of the basic signal; or supplementary, specific, or more detailed meanings of the basic signal. Most complements consist of a single numeral, but there may be two, three, four, five, or six numerals when signaling such values as latitude and longitude, time, or date.

Single-Letter Signals

Signals consisting solely of one letter are used for the most basic messages. Typical ones are listed above. There is also another set of single-letter signals that is used only with numerical complements to communicate azimuth or bearing, course, speed, latitude and longitude, or time and date. Yet another set of single-letter signals, usually made by sound or radiotelephony, is used between icebreakers and assisted vessels.

Two-Letter Signals

The General Signal Code consisting of signals of two letters, many with a single numerical complement, is used for many types of messages. Typical signals are:

Flag	Code	Definition
	AC	I am abandoning my vessel.
	AN	I need a doctor.
	AQ	I have injured/sick person (or number of persons indicated) to be taken off urgently.
	BZ	Job well done.
	CB	I require immediate assistance.
	CK	Assistance is not (or is no longer) required by me (or vessel indicated).
	CP	I am (or vessel indicated is) proceeding to your assistance.
	DV	I am drifting.
	DX	I am sinking (lat...long...if necessary).
	ED	Your distress signals are understood.
	EL	Repeat the distress position.
	fA	Will you give me my position?
	FO	I will keep close to you.
	GW	Man overboard. Please take action to pick him up (position to be indicated if necessary).
	IL	I can only proceed at slow speed.
	IT	I am on fire.
	JG	I am aground; I am in dangerous situation.
	JH	I am aground; I am not in danger.
	JW	I have sprung a leak.
	KJ	I am towing a submerged object.
	KM	I can take you (or vessel indicated) in tow.
	KQ	Prepare to be taken in tow.
	KT	I am sending a towing hawser.
	LB	Towing hawser is fast to chain cable.
	NC	I am in distress and require immediate assistance.
	NF	You are running into danger.
	NG	You are in a dangerous position.
	OQ	I am calibrating radio direction finder or adjusting compasses.
	PN	You should keep to leeward of me (or vessel indicated).
	PP	Keep well clear of me.
	QD	I am going ahead.
	QI	I am going astern.
	QQ	I require health clearance.
	RB	I am dragging my anchor.
	RU	Keep clear of me. I am maneuvering with difficulty.
	TP	Fishing gear has fouled my propeller.
	UY	I am carrying out exercises - keep clear of me.
	YG	You appear not to be complying with the traffic separation scheme.
	ZM	You should send (or speak) more slowly.
	ZS	My vessel is healthy and I request free pratique.

Flag Hoist Signaling

The most common use of the International Code of Signals is visual signaling using code flags. A set of flags consists of 26 flags for the letters of the alphabet, ten number pennants, three substitute pennants, and the answering pennant. (The U.S. Navy uses a fourth substitute and calls them all "repeaters.") The substitutes are necessary because a set contains only one flag for each letter and some flag hoists require repetitions of one or more letters.

Five standard colors are used — red, white, blue, yellow, and black. Most of the flags are of two colors, selected and arranged for maximum contrast. Two flags are of a single color only, three use three colors, and one uses four colors.

Flag hoists are read from the top flag or pennant downward; if there is more than one hoist from a single spreader or yardarm, each hoist is read in turn from outermost inward. Additional details on flag hoist signaling can be found in the International Code of Signals Pub. 102.