Maritime Signal Flags

Maritime Signal Flags.

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:

  • Each flag spells an alphabetic message, letter by 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 (more importantly) 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 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).