Edwin Alexander, American Locomotives, 1900-1950; Bonanza Books 1950
Nicknamed "Old Maud" after a popular cartoon mule of the time, this was the first Mallet (say "mallay" like the French) type articulated locomotive built in the US. It was displayed at the 1904 St Louis World Fair and Exposition, after which it was put to work hauling freight on the grades of western Pennsylvania. It was very successful, basically two locomotives with one crew, leading to the development of bigger and better engines of its type. Old Maud had a thirty year career with the B&O, mostly working as a pusher engine.