The system of international maritime signal flags is one system of flag signals representing individual letters of the alphabet in signals to or from ships. It is a component of the International Code of Signals (ICS). There are various methods by which the flags can be used as signals: 1. Each flag spells an alphabetic message, letter by letter. 2. 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. 3. One or more flags form a code word whose meaning can be looked up in a code book held by both parties. 4. 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". NATO uses the same flags, with a few unique to warships, alone or in short sets to communicate various unclassified messages. The NATO usage generally differs from the International meanings, and therefore warships will fly the Code/Answer flag above the signal to indicate it should be read using the International meaning. Letter flags with ICS meaning: A (Alfa): "I have a diver down; keep well clear at slow speed." B (Bravo): "I am taking in, or discharging, or carrying dangerous goods". C (Charlie): "Affirmative". D (Delta): "Keep clear of me; I am maneuvering with difficulty." E (Echo): "I am altering my course to starboard". F (Foxtrot): "I am disabled; communicate with me." G (Golf): "I require a pilot." H (Hotel): "I have a pilot on board." I (India): "I am altering my course to port." J (Juliet): "I am on fire and have dangerous cargo on board: keep well clear of me." K (Kilo): "I wish to communicate with you." L (Lima): In harbour: "The ship is quarantined." At sea: "You should stop your vessel instantly." M (Mike): "My vessel is stopped and making no way through the water." N (November): "Negative." O (Oscar): "Man overboard." P (Papa): 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): "The way is off my ship." S (Sierra): "I am operating astern propulsion." T (Tango): "Keep clear of me; I am engaged in pair trawling." U (Uniform): "You are running into danger." V (Victor): "I require assistance." 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."