International maritime signal flags are various flags used to communicate with ships. The principal system of flags and associated codes is the International Code of Signals. Various navies have flag systems with additional flags and codes, and other flags are used in special uses, or have historical significance.
There are various methods by which the flags can be used as signals:
A series of flags can spell out a message, each flag representing a letter.
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 and to warn other vessels to keep clear to avoid endangering the diver(s) with their propellers.
One or more flags form a code word whose meaning can be looked up in a codebook 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” (for more details see Race signals).
A – Alpha. Diver below (when stationary); I am undergoing a speed trialB – Bravo. I am taking on or discharging explosivesC – Charlie. (affirmative)D – Delta. keep clear of me, I am manoevering with difficultyE – Echo. I am altering my course to starboardF – Foxtrot. I am disabled, communicate with meG – Golf. I require a pilotH – Hotel. I have a pilot on boardI – India. I am altering my course to portJ – Juliet. I am going to send a message by semaphoreK – Kilo. you should stop your vessel instantlyL – Lima. you should stop, I have something important to communicateM – Mike. My vessel is stoppedN – November. no (negative)O – Oscar. man overboardP – Papa. the Blue Peter – all aboard, the vessel is about to proceed sea. (At sea) your lights are out or burning badlyQ – Quebec. my vessel is healthy and I request free pratiqueR – Romeo. the way is off my ship. You may feel you way past meS – Sierra. my engines are going full speed asternT – Tango. do not pass ahead of meU – Uniform. you are standing into dangerV – Victor. I require assistance (not distress)W – Whiskey. I require medical assistanceX – X-ray. stop carrying out your intentions and watch for my signalsY – Yankee. I am carrying mailsZ – Zulu. to be used to address or call shore stations
