During the early period of World War II, when America was neutral, the government of Franklin D. Roosevelt approved the Lend-Lease supply to the United Kingdom of the S200 Class, a 2-8-2 configuration, designed specifically to fit into the restricted British loading gauge.

[1] With America's entry to World War II, the USATC needed a developed design from which a large number of locomotives could be constructed to run on the wrecked railways of Europe, deploying military hardware and civilian goods.

Hence, the development of the S160 Class, designed by Maj. J. W. Marsh from the Railway Branch of the Corps of Engineers, which drew on previous locomotives, using austerity principles, and was built using methods which allowed for efficient and fast construction, and a long life,[1] including axlebox grease lubricators, and rolled plates in preference to castings.

The larger tender layout was derived from the similar design of the British WD Austerity 2-8-0, with an inset coal bunker above the water tank to improve visibility when running backwards.

The eventual deployment of S160's were: The second batch of 400 S160's were prepared for storage by USATC personnel at the Great Western's Ebbw Junction locomotive depot in the immediate run-up to D-Day.

After the D-Day invasion of Normandy, the locomotives deployed across Britain again began to be collected and be refurbished at Ebbw Junction in preparation for shipment to Europe.