Turks might have employed captured British gear, but automobiles woud be very hard to maintain, and trained drivers plus mechanics rather scarce. I have only one postcard from before 1920 which shows two officers in an auto with mounted machine gun, and it may well be an on-the-spot effort during one of the per-WWI CUP coups. I also have a good shot of Ottoman crews with captured Lewis guns, an indication that your Rolls Royce is not impossible, just improbable. I could not figure how to upload these images, but if you send me an email <jdunn (at) valdosta.edu>, I'll be happy to send them your way.