Hughes in his book  records the following extract:-
The Indian Government was responsible for supplying the expeditionary force to Mesopotamia in World War 1 and, although it was soon decided to adopt the metre gauge for the main routes, the first railway material sent to Basra consisted of 2ft 6in gauge track and rolling stock from the Light Military Reserve Railway maintained by the North Western Railway(NWR); these had previously been used on the temporary lines erected at Delhi in connection with the Delhi Durbar of 1911.
The first shipment arrived in February 1916 and consisted of one mile of permanent way and 100 light trucks of 3-ton capacity, followed in March by three engines and a further 20 miles of track. These were originally used in the Basra area but as the war progressed many miles of 2ft 6in track were laid to cater for urgent traffic requirements. Details of these lines are given in the author's 'Middle East Railways' (Continental Railway Circle, 1981).
The motive power mainly consisted of 14 locomotives from the Military Reserve together with 9 of the similar engines belonging to the NWR itself. In 1917 the main base for the narrow gauge system was at Hinaidi, south-east of Baghdad, from which trains were operated for distances of 20 miles and more. An official account said: 'The narrow gauge engines running on such long leads gave a good deal of trouble as their saddle tanks and bunkers were far too small. To overcome this trouble the engines were run double headed with a bogie, on which were mounted three four-foot cube water tanks, between; a reserve of coal was also carried to replenish the bunkers.'
- “Indian Narrow Gauge Locomotives 1863-1940” by Hugh Hughes, published by ‘The Continental Railway Circle’ Paragraph 39A Page 83