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- “Listen, bud. In the States, we don't care a dime for a few spills.”
The Railway Series
Stanley was built by the Baldwin Locomotive Works sometime around 1917, and apparently worked in the United States before arriving on Sodor. Following the end of the First World War, Stanley was bought secondhand as army surplus by the Mid Sodor Railway and was re-gauged.
Unfortunately, Stanley proved to be a bad bargain. As he had not been re-gauged properly, Stanley was prone to riding roughly along the track and often derailed, though he believed this was no big deal. Repeated attempts to cure this habit failed, and Stanley was stripped of his wheels and became a pumping engine behind the engine sheds at Arlesdale.
Duke later lectured Stuart and Falcon about Stanley's downfall and they became "unusually good for several days". 
Stanley was later relocated to Cas-ny-Hawin to pump out water from the mines, but by December 1946 he was becoming worn-out and broke down, causing the mines to flood. With no reason to stay open, the Mid Sodor Railway was closed and Stanley was scrapped.
Stanley was arrogant and careless and refused to listen to advice. This carelessness eventually led to him being converted into a pumping engine.
Stanley is based on a Baldwin Class 10-12-D 4-6-0 pannier tank engine, built at the Baldwin Locomotive Works in Philadelphia, Pennsylvania, United States for service in the First World War. They were sent to the United Kingdom and the British War Office chose them to be the principal military steam locomotive for the trench railways. However, they were rough riders and had the tendency to derail. After the war ended in 1918, various railways, such as the Welsh Highland and the Snailbeach District Railway acquired them as surplus. Five of these engines are known to be preserved. Stanley had been re-gauged from 1ft 11 5/8in to 2ft 3in.
Stanley was painted red.
- Stanley's second appearance, in the back of the shed in "Bulldog", creates a continuity error. According to "Granpuff", Falcon and Stuart did not know about Stanley, implying Stanley's arrival and likely scrapping occurred before their arrival. However, Stanley is seen in the same shed as Falcon, meaning Falcon would have known about Stanley and what happened to him. Also, it has been confirmed that Falcon was built and came to the railway before Stanley, while Stuart was built and came to the railway before Stanley was turned into a pumping engine.
- Stanley was the first and only engine of an American class in the Railway Series.
- In the illustration of Stanley as a pumping engine, he appears to have a cigarette in his mouth, making this the only time in the Railway Series that something is seen in an engine's mouth.
- In addition, this makes Stanley the only engine in the franchise to be physically seen smoking a cigarette.
- In the illustration of Stanley as a pumping engine, he is incorrectly depicted as a saddle tank and only having one dome. However, it's possible he was given a saddle tank as part of the conversion to a pumping engine, and as he would remain stationary, his sand dome was no longer needed.
- “No. 2", said Duke. "Was American and very cocky. He rode roughly and often came off the rails. I warned him to be careful!"
"Listen, bud!", he drawled. "In the States, we don't care a dime for a few spills!"
"We do here! I said, but he just laughed. But he didn't laugh when the Manager said he was going to take away his wheels and said he was going to make him useful at last."
"W-w-why? What did he do?!"
"He turned him into a pumping engine, that's what! He's still there behind our shed."
Stuart and Falcon were unusually good for several days.”
- ―Duke lecturing Stuart and Falcon about Stanley, "Granpuff", "Duke the Lost Engine"
The Railway Series