The Semaphore (because someone asked.)
From A dictionary of British Ships and Seamen Grant Uden and Richard Cooper, 1980, St. Martin's Press.
Semaphore: system or apparatus for signalling by means of moveable arms, lights or hand-held flags. The term derives from Greek words meaning "sign bearing". A semaphore station was erected at the Admirality Office in London in 1816. see Telegraph
Telegraph, manual: a device for rapid visual signalling, used by the Admiralty from 1796 to 1849 to communicate with the southern naval bases. When it was first set up it depended on the reading of coded messages based on the varying positions of shutters in a frame. The message was sent from Admiralty House and was repeated from hill-top to hill-top down to Deal and Sheerness, and similarly to Portsmouth, and in 1806 it was extended also to Plymouth. The system was replanned in 1816 when a new device, using the semaphore, was introduced from London to Chatham, and a few years later to Portsmouth. Messages could be sent and acknowledged back to the Admirality in a matter of minutes. The system could not of course be worked at night or in fog, but it was of vital importance in the control of the Navy during the NapoleonicWars and later years until it was superseded by the electronic telegraph.