This unidentified WW1 study belonged to John Nash. The inscription on the reverse identifies it as having been drawn in Sinai in 1916. Gilbert Spencer was posted to Sinai during this period – and a life long friend of Nash’s who owned a number of his works.
The Sinai and Palestine Campaign of the Middle Eastern theatre of World War I was fought between the British Empire and the Ottoman Empire, supported by the German Empire. It started with an Ottoman attempt at raiding the Suez Canal in 1915, and ended with the Armistice of Mudros in 1918, leading to the cession of Ottoman Syria and Palestine.