The Austerity Engine is an engine which the Fat Controller planned to acquire to assist Donald and Douglas with their branch line work. In order to assess the abilities of such an engine, he borrowed Wilbert from the Dean Forest Railway for a period in the early 1990s. He told Wilbert that he knew where he could get another engine like him.
The Austerity is an Austerity 0-6-0ST. This type was designed by Hunslet for War Department use in 1943, continued to be built for WD and industrial use until 1964 by various companies. It is unknown which company built this particular Austerity or when it was built. Wilbert and Sixteen are other members of this class. Other members of this class were featured in Thomas and the U.K. Trip and the Down at the Station segments.
Christopher Awdry has confirmed that the engine was intended to be one of the many Austerity 0-6-0STs awaiting restoration around the UK. Contrary to speculation, it was not meant to be Barry, the latter character being confirmed by the author as having been thought up in the 1980s.