Rainer Fuchs’s Iraq railway stamps website has a PDF copy of a wonderful article published by The Railway Magazine in April 1928, entitled The Railways of Mesopotatmia by Richard Coke.
There is also a copy of Rainer’s own article “Iraq Railway Post 1928 – c.1942”, published in the October 2007 issue of The American Philatelist, the monthly publication of the American Philatelic Society.