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The treaty-adopted flag code every seagoing vessel carries.
Also known as: Maritime signal flags, Coloured flags on a ship, Nautical flags
Twenty-six letter flags, ten numeral pennants and three substitutes, with meanings fixed by an instrument rather than by custom. The distinction that makes it usable is between a flag flown alone, which carries a defined message, and the same flag inside a group, which is just a letter.
A published code of forty flags — twenty-six alphabetical, ten numeral pennants, three substitutes and an answering pennant — maintained by the International Maritime Organization and adopted by treaty.
Contexts: Navigation
A flag flown alone carries a defined single-letter message, most of them urgent and about the vessel's own state. Two- and three-letter groups draw on the code book instead, so the same flag means one thing alone and nothing in particular in company.
Reading a group letter by letter as though each carried its single-letter meaning is the commonest way the code is misread.
Designed to be legible at distance, at sea, against sky and water, which is why the palette is restricted to red, white, blue, yellow and black and the designs are large geometric blocks rather than emblems.
It replaced a proliferation of national and company codes during the nineteenth century, so an unfamiliar flag on a historic photograph may belong to a superseded system rather than to this one.
from 1857
Square and swallow-tailed flags and long tapering pennants, each divided into large blocks, crosses, diagonals or borders in red, white, blue, yellow and black.
Alfa is one of the code's twenty-six letter flags.