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Optical “telegraphs” or signaling devices have been traced back to ancient times (using torches). It were the fastest systems to convey messages over long distances.
The semaphore signalling system was designed by Claude Chappe, French engineer, in the late 18th century. First semaphore line was established between Paris and Lille in 1793. Then it was adopted to carry despatches between French army units, including those commanded by Napoleon.
Semaphores were adopted and widely used with hand-held flags in the maritime world. The semaphore system we use today uses flags, usually square and divided diagonally into a red and a yellow section with the red in the uppermost triangle.
The calculator below converts english phrase to the flag semaphore signal sequence: