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International Code of Signals (Overview)

Last modified: 2004-11-13 by
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International Code of Signals (Overview)

The International Code of Signals was first drafted in 1855 by the British Board of Trade and subsequently published in 1857 as a means of maritime communications. The original publication showed 17,000 signals using 18 flags, part of which was specific to the United Kingdom and another part that contained universal signals to be used by all nations. Adopted by most sea-faring nations, the system was revised in 1932 to include seven languages: English, French, German, Italian, Japanese, Spanish, and Norwegian.

The Fourth Assembly of the Intergovernmental Maritime Consultative Organization revised the code in 1965 which became effective on January 1, 1969. This revision added Russian and Greek to the languages already included and adopted a new radiotelephone code. Each signal has a complete meaning.
Jorge Candeias, 31 August 1999


I asked a Flagmakers firm ("Industrial Velera Marsal S.A.") and they make 3 sizes measuring: 1.98x2.41 m, 1.37x1.68 m and 0.76x0.91 m, which they assure are "official". I didn´t find any proportions kept at the 3 sizes. They are close to 8-10, but a little more "squared" than that.

Maritime letter flags, as far as I know, go back to Sir Home Popham, who published "Telegraphic Signals or Marine Vocabulary" in 1800, with a larger version in 1803, and another expanded edition in 1812.

This was used by Nelson to signal his fleet before the beginning of the battle of Trafalgar, the 21 of October, 1805, the famous message: "ENGLAND EXPECTS THAT EVERY MAN WILL DO HIS DUTY". Certainly those flags were 1-1 in proportions and can be seen in several books.

After many manuals and codes, the actual international signal flags developed from Captain Frederick Marryat´s "Code of Signals for the Merchant Service".

This actual international code is what we need to find out if it has construction sheets.

In Whitney Smith´s 1975 book, page 86, letter flags are drawn in prop. 8-10.
Jose C. Alegria, 25 August 1999

I am not a specialist of signal flags (Album des Pavillons presents all national flags, ensigns and markings at sea, but not signal flags) yet I had a look at the technical specifications of French Navy and British Royal Navy : signal flags have the following measures (in cm).
French Navy 198 : 244
137 : 168
76 : 91
British Navy 183 : 229
114 : 152
102 : 122
61 : 76
46 : 53
30 : 38
Armand Noel du Payrat, 25 August 1999
Here are the correct proportions for the International Ship Code Flags: Robert Lloyd Wheelock, 25 August 1999

In Flags at Sea, Timothy Wilson wrote; "The most common sizes for signal flags of the International Code nowadays (1986) are: 78 inches by 96 inches, 54 inches by 66 inches, and 30 inches by 36 inches."

The sizes offered in a current catalogue are (all in inches): 9x12, 12x18, 18x21, 24x30, 30x36, 43x54, 48x72.

Marryat suggested that his flags should be 6 feet by 8 feet, with pennants 4 feet by 18 feet.
David Prothero, 28 August 1999

The US Navy page on signal flags, also shows what look like 1:1 proportions. Although the depiction of the "Romeo" flag looks to me like the cross is too narrow, so use your best judgment on reliability of the other representations. The page also shows United States Navy vs. international meanings of individual flags, for those interested.
Joseph McMillan, 31 August 1999

I visited the Bornholm Museum in Rønne, on Bornholm, during my vacation, and they had this overview of the signaling flags in different version of the code. Signaling flags being an interest of mine, I just had to jot them down:

If I'm deciphering my all-too-small notes correctly, the 1867 version had:

B   Like the current flag
C   White with a red dot (as the current "1", but shaped more or less like the current repeaters)
D   Blue with a white dot (as the current "2", but the same shape as its "C")
F   Red with a white dot (its "C" in reverse)
G   Yellow before blue  (as the current "K", but shaped like its "C", and with the 
    yellow only approx. 2/5 of its length)
H   Like the current flag
J   Like the current flag
K   Like the current flag
L   Quartered blue and yellow
M   Like the current flag
N   Like the current flag
P   Like the current flag 
Q   Like the current flag
R   Like the current flag
S   Like the current flag
T   Like the current flag
V   Like the current flag
W   Like the current flag

Answering pennant Like the current flag (However, I'm not sure about this one: Other sources, displaying the 1901 code picture a sharp-tipped flag, like the "C" in this code.

I knew there were no vowels in this code, but it turns out there were no X or Z either. Well, considering that the code started out as English [It did, didn't it?], and these letters are basically non-native for English, this might make sense.

OK, returning to my notes, and the di Pietri system, these were the changes to the flags in 1901:

A   Like the current flag
E   Columns of red, white and blue (like the "T", but shaped like its "C") 
F   Red with a white cross (shaped like its "C")
I   Like the current flag
L   Like the current flag
O   Like the current flag
U   Like the current flag
X   Like the current flag
Y   Like the current flag
Z   Like the current flag

Adding the missing letters. The "F" is changed to avoid confusion with the other dark-coloured pennant with white dot, I expect. Why did they change the "L"? Maybe a partly folding "L" would look too much like a "K"?

In 1933 all changed to their current flags. The pennant shaped letters were replaced. The digit pennants, with their obtuse tips, were introduced, as well as the repeaters. [How did they repeat before this, then? Or was the code build to avoid repetition?] From now on the answering pennant seems to have its shape like a slightly longer version of a digit pennant.

The chart didn't mention any other signals. If the black wreck flag was ever part of the code, it wasn't shown here, nor did it show when any of the other signal flags were introduced.
Peter Hans van den Muijzenberg, 10 August 2003

Comparing the 1913 International Signals Code depicted therein with the current ICS, I noted that the flags for the letters C, D, E, F and G are pennants. At some point the rectangular flags with the quite different designs that they are in the current International Code of Signals. All the other alphabetical flags of the 1913 code are still the same in the current ICS.

Incidentally, these five pennants with their designs survived in the modern ICS as the numeral pennants 1,2,3,4 and 5.
Andre Burgers, 8 September 2004

The change came into force on 1st January 1934. In the previous 1901 Code the alphabet flags were used to represent numbers, from 2 to 27. 1934 was also when the three substitute flags were introduced.
David Prothero, 9 September 2004