just been informed about this interesting monorail ....
light re-supply Monorail .... "the rail was up in the air five to six feet on 4" dia. poles driven into the ground & was therefore very easy to install, run and repair over rough, broken or shell shot ground."
Known as the "Irish Pattern Monorail" invented by Captain Finnimore R.E. and described as a version of the French Lartigue track system but not requiring the two balancing rails that would normally be mounted further down the pole. Very small & powered by a motorcycle engine, it was said to carry 400 lbs plus driver ! Presumably it was to supply ammunition & supplies to the very front lines until the battle stabilized & a regular narrow-gauge rail system could be laid.
A drawing is in the book "Railways and War before 1918" by Denis Bishop & WJK Davies (MacMillan) - several on Amazon. The other monorails mentioned are all civilian.
I'm guessing that it was never actually built or used but there may be plans or a patent in UK archives ?