An operator, opening and closing the shutter, could produce short and long flashes to spell out messages in Morse code..
It employed two adjustable mirrors so arranged that a beam of light from the sun could be reflected in any direction.
Later Sir Home Popham increased the effectiveness of ship-to-ship communication by improved methods of flag signaling. The development of the of dots and dashes used with key and sounder was soon used to augment the various means of visual signaling.
Vice Admiral Philip Colomb’s flash signaling, adopted in the British navy in 1867, was an adaptation of the Morse code to lights.
Immediately before and during the Civil War visual signaling also received added impetus through development of a system, applying the Morse code of dots and dashes, that spelled out messages with flags by day and lights or torches by night.
Field and switchboards were soon developed, and those already in existence were improved.Before the end of the 18th century European armies used the visual telegraph system devised by towers or poles with movable arms.The Prussian army in 1833 assigned such visual telegraph duties to engineer troops.At the same time that these elementary methods of signal communication were being evolved on land, a comparable development was going on at sea.Early signaling between naval vessels was by prearranged messages transmitted by , lights, or the movement of a sail.