Although not visible at any of the sites today, arguably the most important element of the signal stations was the signal mast itself. These were 50ft (15.25m) tall masts that supported rigging from which would be suspended a series of flags and ‘balls’ which communicated a series of preset messages, or which could be used to laboriously spell out individual letters and numbers that combined to make bespoke messages. With the signal stations spaced out at 7 to 14 mile (11.25 to 22.5 km) intervals the signal masts could only be read using a telescope, which along with the code book, would have been two of the most valuable items held at each signal station.
During the late 18th century and early 19th century communications technology began to develop at a considerable pace, having been largely static for hundreds of years previously. Perhaps the most important breakthrough was that of Claude Chappe who invented the movable arm ‘T’ telegraph system in 1792 and which was rapidly adopted across post-revolutionary France, and its conquered territories, from 1794 onwards. The ‘T’ telegraph allowed rapid changes to be made to the signal arms meaning that complex codes consisting of combinations of numbers could be transmitted with considerable speed. Similar systems were quickly adopted in England, Sweden and a number of other European countries.
The Irish signal stations utilised a curious mixture of old and new technology. The idea of long distance signal chains capable of sending complex messages was new, and mirrored the developments in France and in England where ‘shutter’ telegraphs were built to connect the Admiralty buildings in London to the important naval dockyards on the south and east coasts. However the signalling system used was an older concept developed by both naval and mercantile shipping in the mid 18th century and which has its ultimate origins in the simple flag signals used by boats during the medieval period. These flag based systems came in both ship to ship and ship to shore varieties and involved hanging flags and other items onto either the ships rigging or onto special masts constructed at prominent points along the coast. Although in use for a long period these initially simple systems became increasingly elaborate during the second half of the 18th century.
As the information that these flag signals were required to transmit became increasingly complicated there was a need for standardisation and rationalisation of the different systems being used. For the British Navy this was achieved in 1799 when Rear Admiral Home Riggs Popham published his first list of telegraph signals. Popham’s code underwent several revisions and a mercantile variant, Marryat’s code, was published in 1817. A series of singular ship to shore signal posts had been established along the southern coast of England prior to the establishment of the more complex shutter telegraph systems.
The Irish Signal Stations utilised a variation of these older style of flag systems, connected together in a long distance chain. Whilst it might seem a little anachronistic given that the more sophisticated shutter telegraph system was already in use in England, these flag signal systems continued to develop throughout the 19th century and very much remained a ‘current’ technology. The continued dominance of the British Navy during the early part of the 19th century relied to some degree on the Navy’s mastery of these flag signals which allowed their ships to be organised into precise formations, as seen most famously at the Battle of Trafalgar.
The Irish signal stations were crewed with former sailors who would have been familiar with these flag signalling systems. The introduction of a more modern system would have necessitated more training and the use of more specialised and expensive equipment.
The signal station at Malin Head in Donegal was refurbished in 1884 by Lloyds of London to communicate with ships passing the northern coast of Ireland. In 1902 the signal station housed an experimental Marconi radio relay but because many ships were not fitted with radios, flag signals continued to be used for some time after radios were invented. In the above photograph flag signals are being flown in celebration of the introduction of the radio relay, but it was the development in electrical and radio telegraphy that eventually saw flag signals become a redundant technology.
For more details about the signal stations click here.