Sir Madog (Ulrich):
The following link is to a Forum Thread that was opened in November of 2011:
"Military Railways from the WWI Era (France)"
http://cs.trains.com/trn/f/740/t/199499.aspx
It went out to some three pages, with a number of external links for a pretty interesting discussion of the WWI Trench Railways. Many of the locomotives were supplied in kit form by Baldwin Locomotive Works and assembled in the ETO by the Troops.
Hope you’ll enjoy it!