International maritime signal flags
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 with their propellers.
- 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".
During the Allied occupations of Axis countries after World War II, use and display of those nations' national flags was banned. In order to comply with the international legal requirement that a ship identify its registry by displaying the appropriate national ensign, swallow-tailed versions of the C, D, and E signal flags were designated as, respectively, provisional German, Okinawan, and Japanese civil ensigns. Being swallowtails, they are commonly referred to as the "C-pennant", "D-pennant", and "E-pennant".
Letter flags (with ICS meaning)
| Letter/ phonetic name | Flag | ICS meaning as single flag | Meaning when used with numeric complements |
| A Alfa | "I have a diver down; keep well clear at slow speed." | Azimuth or bearing | |
| B Bravo | "I am taking in or discharging or carrying dangerous goods." | ||
| C Charlie | "Affirmative." | Course in degrees magnetic | |
| D Delta | "Keep clear of me; I am maneuvering with difficulty." | Date | |
| E Echo | "I am altering my course to starboard." | ||
| F Foxtrot | "I am disabled; communicate with me." | ||
| G Golf | "I require a pilot."By fishing vessels near fishing grounds: "I am hauling nets." | Longitude Morse signaling by hand-flags or arms;2) Loud hailer Morse signaling lamp;4) Sound signals. | |
| L Lima | "You should stop your vessel instantly." | Latitude | |
| M Mike | "My vessel is stopped and making no way through the water." | ||
| N November | "Negative." | ||
| O Oscar | "Man overboard.".With a sinister hoist, the semaphore flag. | ||
| P Papa | The blue Peter.In harbour: 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 | Distance in nautical miles. | ||
| S Sierra | "I am operating astern propulsion." | Speed in knots | |
| T Tango | "Keep clear of me."Fishing boats: "Keep clear of me; I am engaged in pair trawling." | Local time. | |
| U Uniform | "You are running into danger." | ||
| V Victor | "I require assistance." | Speed in kilometres per hour. | |
| 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."By fishing vessels near fishing grounds: "I am shooting nets." | Time. |
Notes
Number flags
Substitute
Substitute or repeater flags allow messages with duplicate characters to be signaled without the need for multiple sets of flags.The four NATO substitute flags are as follows:
| First substitute | Second substitute | Third substitute | Fourth substitute |
The International Code of Signals includes only the first three of these substitute flags. To illustrate their use, here are some messages and the way they would be encoded:
| "N" | - | - | - | - | |
| "O" | - | - | - | - | |
| "NO" | - | - | - | ||
| "NON" | - | - | |||
| "NOO" | - | - | |||
| "NOON" | - | ||||
| "NONO" | - | ||||
| "NONON" | |||||
| "NONNN" |