In 1815, Admiral Sir Home Riggs Popham developed a type of two-armed semaphore that could be used on water and land. The mast had a height of 30 feet; the arms were each 8 feet long.
The arms were attached at about 4m height or at the top. When at rest, they ran parallel to the mast.
The arms could be arranged in six positions each, giving 36 different signals.
The telegraph was designed to rotate so that signals could be sent to passing ships.