Ottoman heliograph crew at Huj during World War I, 1917.

“A Heliograph (Greek: Ἥλιος helios, meaning “sun”, and γραφειν graphein, meaning “write”) is a wireless solar telegraph that signals using Morse codeflashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter. The heliograph was a simple but highly effective instrument for instantaneous optical communication over 50 km or more in the late 19th and early 20th century. Its major uses were military, survey and forest protection work. Heliographs were standard issue in the British and Australian armies until the 1960s, and were used by the Pakistani army as late as 1975.”

And a Central Asia connection: 

“The Red Army made use of chains of heliograph stations to efficiently disseminate intelligence about basmachi rebel movements in Turkestan in 1926 during the Russian Civil War. ^[9]”