In 1937 the Birmingham Southern Railroad took delivery of two 900-horsepower diesel switchers from the American Locomotive Company. Popularly styled the HH ("high hood") series, this type was Alco's first production-model diesel switcher, being replaced in 1940 by the S series. This builder's photo, supplied by Wayne Koch, couples HH900 units 81 and 83 back to back; however, photos indicate they did not always operate in that fashion. Sister unit 82 is preserved at the Heart of Dixie Railroad Museum in Calera, Alabama.