The ten locomotives were built in one batch, and were numbered 686 to 695. They were designed for the Scarborough to Whitby line, on which the Class O0-4-4T locomotives then in use were having difficulty with the traffic, especially the three-mile (4.8 km) section of 1 in 40 (2.5%).[2] However, the low fuel and water capacity was a barrier to operational efficiency, and so between September 1914 and January 1917 the whole class was rebuilt as 4–6–2T locomotives and reclassified W1.
Only one batch was built as the design was soon superseded by the Class D4-4-4T.