International Code of Signals
I went to sea in 1951 after graduating from Haifa Nautical School, where the Signals Course contained Morse, Semaphore and International Code of Signals. I do not recall ever being in a position where ICoS communication took place.
In 1967, as Operations Manager for Maritime Fruit Carriers, I produced a ship-to-office company private code that contained hundreds of phrases, each one represented by five letters. It covered all aspects of ship operation. The idea was to save on cost of cables and it worked very well.
In 1993 I published (In Israel, in Hebrew) a maritime thriller entitled "Ship of Prey” and based on a true maritime fraud which took place in the 1960s. The clue to the mystery in that thriller was a two-flag hoist of code flags that was erroneously hoisted up side down, giving the message an entirely different meaning. I remember I used Vol. I of the 1931 code book in searching for the suitable code messages for my story. That Code Book came in two red volumes, which unfortunately I donated to the library of a certain institute that does not exist anymore.