The NBR S Class (LNER Class J37) is a class of 0-6-0 steam locomotive designed by William Paton Reid for freight work on the North British Railway. The engines were initially designated as B class, being a development of the standard B class locomotives designed by Reid some eight years previously, and represented the culmination of a long evolution on the NBR of powerful 0-6-0 freight engines. The new locomotives were introduced in 1914 and had superheaters, inside cylinders and piston valves operated by Stephenson valve gear.