Signal Code
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Background
Sea signals are used on ships to communicate with each other or with stations on shore when in sight of land. They use a system of flags of different colours and shapes. Sea-signals are still in use today, even with the advent of modern communications such as satellite telephones. Less than a century ago they were the primary means of communication at sea.
In the year 1803 Sir Home Popham introduced a system into the Royal Navy a system of flag signal codes. Sir Popham's system utlised a set of different coloured flags that represented the numerals from 0 to 9. By combining four of these flags together, 10,000 different numerals from 0000 to 9999 could be generated with flags and hoisted in the ship's rigging.
Each letter of the alphabet was represented by a numeral as were the most common words and sentences in use in Naval communications at that time. These codes were included in special signal books so that one ship's crew could hoist a set of flags with a coded meaning, and the crew of another ship could read the flags and decode them by referring to the signal book. Each of these words and sentences were arranged alphabetically in the signal code book so that the correct numeral and flags could be chosen, as well as also being arranged numerically in the book so that the flags could be decoded.
It was this system that Nelson used to address his fleet at Trafalgar when he hoisted his famous signal:
| England | expects | that | every | man | will | do | his | d | u | t | y |
| 253 | 269 | 863 | 261 | 471 | 958 | 220 | 379 | 4 | 21 | 19 | 24 |
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Note: Due to a peculiarity of that part of the code used to send the letters of the alphabet, the word "duty" appears to be mis-spelt. "T" the 20th letter of the alphabet was signalled "19", because the alphabet had been reduced to 25 letters and "I" and "J" were both signalled by "9". This moved all subsequent letters up one number. However "U", the 21st letter was signalled "21", because in the alphabet it was listed after "V".[1]
The limited scope of this system led to its abandonment, however the principle of the Sir Popham system lived on. In 1839, the Royal Navy introduced a new signal system based on flags for the 26 letters of the alphabet. Whereas four numeral flags offered 10 x 10 x 10 x 10 = 10,000 permutations, the alphabet system offered 26 x 26 x 26 x 26 = 456,976 permutations for the equivalent use of four flags.
Probably the most frequent subject of communication at sea to this day is the name of a ship. However as is the case with names of people, some ship names such as 'Mary' or 'Jane' or 'John' can be particularly common.
In order to ensure positive identification of ships it was necessary to include details such as the ship's port of registry, register number and year of registry. This would require hoisting a series of signals to try to identify a ship. It also happened that ships would be sold, based in a new port, reregistered, and given new names and/or registration numbers and thus the very character of the ship would change.
This problem was remedied in 1854 with the British Merchant Shipping Act which required every ship to have a distinct official number that was permanently marked on the ship. With every ship having a unique number, and an authoritative Mercantile Navy List published annually with monthly supplements, listing the numbers and details of the ship, it was possible to positively identify a ship by its official number. If this official number could be displayed with a set of signal codes, then ships would be able to positively identify each other at sea.
In 1817, the merchant navy had adopted a similar numeral-based signal flag system to that of the Royal Navy. It was devised by a naval officer called Captain Maryatt. However it too was found to be inadequate as commerce increased and in 1855 the British Board of Trade appointed a committee to develop a new set of signals. What they came up with was a system of eighteen codes flags representing the eighteen consonants of the English alphabet. By allocating a four letter code to every ship, and listing these too in the Mercantile Navy List for each ship, it was easy for a ship to identify itself by hoisting four flags in a single hoist.
In the case of the City of Adelaide, when she was built in 1864 and registered, she was assigned the official British Registration number 50036 and signal WCLQ.[2]
References
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