Philthydirtyanimal has an impressive Flickr collection of “Photos of stuff from The Great War. Photos of stuff from revolutions. Photos of stuff I find interesting”.
This beast certainly falls into two categories. The photo was apparently taken in Mesopotamia during World War I.
According to a discussion on the Landships forum, it is an Indian Pattern Fiat called HMAC Malaya. “There was certainly an Indian Pattern Fiat, adapted to run on rails, in the area! Along with at least two Austin 3rd Series, also adapted for rail work, it formed part of the Railway Armoured Motor Battery. Operated on the line between Basra and Baghdad.”
The Landships forum also has a picture of some motorised rail ambulances.