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. United States Power Squadrons Flag and Etiquette Committee Signal Flags
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.
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 . Being swallowtails, they are commonly referred to as the "C-pennant" (German: C-Doppelstander), "D-pennant", and "E-pennant".
| +Letter flags and ICS meanings |
Notes
| +NATO number flags |
The four NATO substitute flags are as follows:
| Fourth substitute | ||||
| Blazon | Triangular, or, a bordure azure which does not touch the dexter end | Triangular, per pale azure and argent | Triangular, argent, a fess sable | Triangular, gules, a square or in the fess position touching the dexter end |
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:
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