Substitute flag

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).[1]


There are various methods by which the flags can be used as signals:

  • each flag spells an alphabetic message, letter by letter.
  • individual flags have specific and standard meanings;[2] for example, diving support vessels raise the "A flag" indicating their inability to move from their current location because they have a diver underwater.
  • 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" (for more details see Race Signals).

Code/Answer flag above the signal to indicate it should be read using the International meaning.

During the allied occupations of Axis countries after World War II, use and display of those nations' national flags were 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" (C-Doppelstander), "D-Pennant", and "E-Pennant".

Letter flags (with ICS meaning)


Additional meanings

Flag NATO Nations Naval Meaning - Replenishment at Sea
Romeo Romeo at Dip: Romeo flag is located 34 way up toward the point of the hoist. On the control ship, it means, "I am steady on course and speed and am prepared to receive you alongside on side indicated." On the approaching ship, it means, "I am ready to come alongside."
Romeo Close Up: Romeo flag is at the top of the hoist, touching the point of the hoist or as high as it will go. On the control ship, it means, "I am ready for your approach.: On the approach ship, it means, "I am commencing my approach."
Romeo Hauled Down: This means the first messenger is in hand for controlling and receiving ship.
Bravo Bravo at Dip: Bravo flag is located 34 way up toward the point of the hoist. On the delivery ship, it means, "I have temporarily stopped supplying." On the receiving ship, it means, "I have temporarily stopped receiving."
Bravo Close Up: Bravo flag is at the top of the hoist, touching the point of the hoist or as high as it will go. On both ships, it means fuel or explosives are being transferred.
Bravo Hauled Down: On both ships, it means delivery is complete.


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:


See also


External links

  • "How Ships Talk With Flags", October 1944, Popular Science
  • John Savard's flag page. Collection of different flag systems.
  • Freeware to aid memorizing the flags
  • Esperanto language - the flags for the Esperanto letters with diacritical marks have the lighter color in the normal flag replaced with light green, which is not used in any normal flag.
pl:Międzynarodowy Kod Sygnałowy
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.