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"Stand by to Copy"

A term deriving from the Greek words meaning "sign bearing", semaphore is a centuries-old system of visual communication using flags or lights.

Both the ancient Greeks and Romans are known to have signalled over short distances with torches and flags. With the invention of the telescope in the 17th century, the range of such systems greatly increased. By 1794, a French engineer by the name of Claude Chappe took advantage of telescope technology to devise a semaphore that employed a series of poles placed on rooftops or towers.

Credit:  MCpl Colin Kelley A naval communicator aboard HMCS TORONTO passes information by semaphore during a replenishment at sea with a supply ship.

Developed for Napoleon during the French Revolution, this innovation to the semaphore mounted a pivoted beam with arms at the top of a series of towers built 8 to 16 kilometres apart. A telescope was placed at the top of each tower so that operators could relay the signals back and forth. The result was a communications system that allowed the French military to carry a message a total of 240 kilometres from Paris to the city of Lille in two minutes. By comparison, the alternative was a rider on a horse that would take 30 hours to travel the same distance.

This same system was exported to Britain by the reverend Lord George Murray where a similar series of towers was built from London to Chatham, and a few years later to Portsmouth, the Royal Navy's primary naval base. While the system could not transmit messages at night or during fog, it became of vital importance in communicating directives from the Admiralty in a matter of minutes.

Eventually this system was adapted for communications at sea and at the beginning of the 19th century Rear-Admiral Sir Home Popham developed the first alphabetic system of flag signalling. Flags one through nine were assigned to letters A through J with two-flag hoists accounting for the rest of the alphabet. RAdm Popham's code included a numbered dictionary of 3 000 predefined words and sentences, plus the capability to spell out words not included in the dictionary. Easily the most famous signal transmitted using RAdm Popham's code was Lord Nelson's historic message in the Battle of Trafalgar: "England expects that every man will do his D-U-T-Y", with the letters of the word 'duty' each spelled separately, as it was the only word in Lord Nelson's directive not included in the predefined hoists.

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