The Solar Topee or Pith helmet - made as the name suggests from plant material. I believe that the British ones were generally fabric-coverd cork.
The location of the WD16Hs is identifiable as Egypt, if nothing else by the fitment of bulb horns. As late as 1940 these were still being listed in the VAOS (Vocabulary of Army ordnance Spares) for fitment in Egypt only.
I assume that this was based on a requirement of the Egyptian authorities and that electric horns were in some way not considered adequate. Did they scare the camels ?)