The Belgians had designed gauge 2′C n2t locomotives as early as in 1900–1901 for Chemins de Fer du Calvados. The prototype was Tubize factory type 73. Weidknecht used these drawings and built similar 11-ton locomotives with subcontracted boilers, presumably built by S.A.Energie, Marcinelle. The French military circles became interested in this 2′C n2t locomotive type for their Decauville Light Military Railways in Morocco. A little heavier 14-ton type was designed and an order was placed for Weidknecht to produce these locomotives for the gauge lines in Morocco. Weidknecht delivered 10 more in 1913 for Chemins de fer Militaires du Maroc numbered.
Baldwin built locomotives
For the French Government
When the Great War broke out in August 1914 the French lost most of their locomotive building capacity in the Northern France to German occupied area. Therefore, the French Army demanded fast replacement of the locomotive building capacity for their useful 2′C n2t type which had proved to be a reliable locomotive type for the lightly laid military railways. Three steam locomotive type drawings were sent to Baldwin Works for production of C n2t, 2′C n2t, and light Mallet B′B n4v for gauge lines. With the usual American liberty, Baldwin Drawing Office produced their "version Americaine" of these locomotive types. The first C n2t came out in November 1914 and the first batch of 2′C n2t in January 1915. Only two more batches were built for the French.
The British War Office decided to adopt the type as its principal military steam locomotive, and Baldwin started production in 1916, building 495 locomotives between October 1916 and April 1917. All were delivered except for nine which were lost at sea.
Use outside Europe
Some of the class found during war their way to other theatres of war than Europe. Baldwin 45163–45222 from batch No 1001–1104 were renumbered by the British War Office to War Department Light Railways, Middle East No 581–640 and were shipped to Egypt to be used in Sinai and Palestine during the British 1917 offensive against the Turks. After the war most of them remained in Middle East.
Peacetime service
After the war many of these locomotives were sold and went on to work in France, Britain and India. Indian North Western Railway received fifty locomotives, numbered NWR No 1–50, many of which later operated at sugar mills in various parts of the country. British narrow-gauge railways which used them included:
No. 778 is operational at its home base, No.794 is undergoing contract restoration at the Vale of Rheidol Railway for the WHHR, works No. 45190 is currently visiting the Ffestiniog and Welsh Highland Railways, and works No. 44657 is awaiting restoration, also at the SBR. One other locomotive is preserved on the Dreamworld Railway in Coomera, Queensland, Australia. This locomotive worked on a sugar mill in Mackay and prior to the opening of Dreamworld in 1981 after purchase was heavily modified, including a tender, Wild-West style chimney, and conversion to oil-firing. It is currently under overhaul.
In fiction
The fictional No. 2 in The Railway Series by the Rev. W. Awdry was based on this engine.
Models
Bachmann Branchlines have produced the Baldwin Class 10-12-D in 009 gauge in 10 liveries with liveries including War department livery, Ashover light railway, Glyn Valley Tramway, Snailbeach District Railway, Southern Railway and Welsh Highland railway liveries. Minitrains also produce models of the Baldwin class 10-12-D class.