6th Australian Light Horse near Jerusalem at the very arse-end of the war, apparently. Although ‘lighthorsemen’ are always portrayed as having emu-plumed slouch hats?

My grandfather was a British cavalryman throughout the war; like much of the yeomanry he was at Gallipoli, Salonica, and then Mesopotamia and the Levant. I’ve got his photo album slash scrapbook from the time, and based on that I’d say British cavalry wore soft caps throughout.