How flag semaphore works
A signaller holds one flag in each hand and extends both arms to spell out letters, one at a time. Each arm can point in one of eight directions - up, down, out to the side, or one of four diagonals - arranged like the hours of a clock around the body. A letter is simply the combination of where the left arm points and where the right arm points.
Where did flag semaphore come from?
Flag semaphore grew out of the mechanical semaphore towers used across Europe from the late 1700s, adapted for ships and sailors who needed a way to signal over open water without a tower in sight. It remained standard maritime and military signalling for over a century, long before radio made it largely ceremonial.
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