Maritime Signal Flags Guide – International Code & Racing

The ICS Flag System

The International Code of Signals (ICS) is a standardised system of flags used by vessels worldwide. Each flag represents a letter of the alphabet, and when flown singly, carries a specific meaning understood in any language.

The system includes:

26 alphabet flags (A–Z) — each with a unique design and a single-flag meaning
10 numeral pennants (0–9) — triangular flags for numbers
3 substitutes (repeaters) — used to repeat a flag already in the hoist
1 code/answer pennant — used to acknowledge signals or indicate a message follows the ICS code

In dinghy sailing and yacht racing, signal flags are used extensively by race committees. Understanding flags like P (Preparatory), AP (Postponement), and individual recall signals is essential for competitive sailing.

Each flag flown alone has a unique meaning. For example, Alpha (A) means "I have a diver down; keep well clear at slow speed." These single-flag meanings are internationally agreed and need no codebook to interpret.

Match the flag fact

Item

Alphabet flags

Numeral pennants

Substitute flags

Code/Answer pennant

Count

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Alphabet Flags A–M

Flag	Phonetic	Colours	Single-flag meaning
A	Alpha	White & blue swallow-tail	I have a diver down; keep well clear at slow speed
B	Bravo	Red (solid)	I am taking in, discharging, or carrying dangerous cargo
C	Charlie	Blue, white, red, white, blue horizontal stripes	Yes / Affirmative
D	Delta	Yellow, blue, yellow horizontal stripes	Keep clear of me; I am manoeuvring with difficulty
E	Echo	Blue & red horizontal halves	I am altering my course to starboard
F	Foxtrot	White with red diamond	I am disabled; communicate with me
G	Golf	Yellow & blue vertical stripes (6)	I require a pilot
H	Hotel	White & red vertical halves	I have a pilot on board
I	India	Yellow with black circle	I am altering my course to port
J	Juliet	Blue, white, blue horizontal stripes	I am on fire and have dangerous cargo: keep clear
K	Kilo	Yellow & blue vertical halves	I wish to communicate with you
L	Lima	Yellow & black quartered	Stop instantly (in harbour: vessel is quarantined)
M	Mike	White with blue X	My vessel is stopped and making no way

The most critical flags to know immediately: A (diver down), B (dangerous cargo), O (man overboard), and V (I require assistance). These are safety-critical in any waters.

Key flags A-M — tap to reveal

A — Alpha

White & blue swallow-tail. "Diver down — keep clear at slow speed"

B — Bravo

Solid red. "Dangerous cargo on board"

F — Foxtrot

White with red diamond. "I am disabled; communicate with me"

H — Hotel

White & red vertical halves. "Pilot on board"

L — Lima

Yellow & black quartered. "Stop instantly"

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Alphabet Flags N–Z

Flag	Phonetic	Colours	Single-flag meaning
N	November	Blue & white chequered (4x4)	No / Negative
O	Oscar	Red & yellow diagonally divided	Man overboard
P	Papa	Blue with white centre square	About to put to sea (in racing: preparatory signal)
Q	Quebec	Yellow (solid)	My vessel is healthy; I request free pratique
R	Romeo	Red with yellow cross	No specific single-flag meaning in ICS
S	Sierra	White with blue centre square	I am operating astern propulsion
T	Tango	Red, white, blue vertical stripes	Keep clear; engaged in pair trawling
U	Uniform	Red & white quartered	You are running into danger
V	Victor	White with red X	I require assistance
W	Whiskey	Blue with white centre cross	I require medical assistance
X	X-ray	White with blue cross	Stop your intention and watch for my signals
Y	Yankee	Yellow & red diagonal stripes	I am dragging my anchor
Z	Zulu	Black, yellow, red, blue triangles	I require a tug (in racing: shore signal)

N over C (November over Charlie) is the international distress signal by flags. It means "I am in distress and require immediate assistance." This two-flag hoist is recognised worldwide.

Match the flag description to its letter

Description

Red & yellow diagonal

Blue, white centre square

White with red X

Blue & white chequered

Red & white quartered

Flag letter

Drop here

Section complete!

Number Pennants & Substitutes

Numeral pennants are triangular (tapered) flags used to signal numbers. They are used in combination for course numbers, race signals, and identification.

Number	Colours
0	Yellow & red vertical halves
1	White with red centre dot
2	Blue with white centre circle
3	Red, white, blue vertical stripes
4	Red with white cross
5	Yellow & blue vertical halves
6	Black with white diagonal stripe
7	Yellow & red horizontal stripes
8	White with red cross
9	White, red, yellow, black horizontal quartered

Substitute (repeater) flags allow you to repeat a flag that has already been used in the same hoist, since only one of each flag exists in a set:

1st Substitute — repeats the first flag in the hoist
2nd Substitute — repeats the second flag
3rd Substitute — repeats the third flag

For example, to signal "11" you would hoist numeral pennant 1 followed by the 1st Substitute.

The Code/Answer Pennant has vertical red and white stripes. When hoisted by itself, it means "I understand your signal." When used with ICS code groups, it indicates the message uses the International Code of Signals.

Fill in the blanks

Numeral pennants are ___ in shape. To signal "22" you would use pennant 2 followed by the ___. There are ___ substitute flags in total.

Triangular

1st Substitute

Rectangular

3

2nd Substitute

Section complete!

Common Flag Combinations

While single flags have standard meanings, many important signals use two or more flags together. Here are the most important combinations:

Signal	Flags	Meaning
NC	November + Charlie	Distress signal — I am in distress and require immediate assistance
AP	Answering Pennant	Race postponed (in racing context)
AP over H	AP + Hotel	Race postponed — further signals ashore
AP over A	AP + Alpha	Race postponed — no more racing today
X flag	X-ray (alone)	Individual recall — one or more boats over the line at the start
1st Substitute	1st Sub (alone)	General recall — all boats return, the start is abandoned
N over A	November + Alpha	Abandonment — all races are abandoned (return to shore)

Racing start sequence (common RYA club racing):

Warning signal — class flag displayed (5 minutes to start)
Preparatory signal — P flag (Papa) displayed (4 minutes)
One-minute signal — P flag removed (1 minute)
Start — class flag removed (0 minutes)

Flag O (Oscar) means "man overboard" when flown alone. In a race, if you see this flag on a committee boat, be alert — a rescue is underway and you must keep clear of the rescue area.

Racing flag signals — tap to reveal

P flag (Papa)

Preparatory signal — shown at 4 minutes before start

X flag (X-ray)

Individual recall — one or more boats were over the line

1st Substitute

General recall — the start is abandoned, all boats return

AP (Answering Pennant)

Race postponed — wait for further signals

N over C

International distress signal — I require immediate assistance

N over A

All races abandoned — return to shore

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