Flags have long been used to identify a ship’s nationality and to convey clear messages. Flags of different patterns and colours form an internationally recognized code for the letters of the alphabet and each also has a meaning of its own when flown individually. They are shown below.
International code
A: I am undergoing speed trials.
B: I have explosives on board.
C: Yes.
D: Keep clear, I am in difficulties.
E: I am altering course to starboard.
F: I am disabled.
G: I require a pilot.
H: Pilot is on board.
I: I am altering course to port.
J: I am sending a message by semaphore.
K: Stop at once.
L: Stop, I wish to communicate with you.
M: A doctor is on board.
N: No.
O: Man overboard.
P: (The Blue Peter): I am about to sail.
Q: Quarantine flag.
R: I have stopped.
S: I am going astern.
T: Do not pass ahead of me.
U: You are in danger.
V: I need help.
W: Send a doctor.
X: Stop, and watch for my signals.
Y: I am carrying mails.
Z: I am calling a shore station.