Well-done history of the development of the Pennsy Q Class, perhaps the most powerful steam locomotive ever. Explains its origins at the Baldwin Locomotive Works, the B&O's Q1, and its adoption by the Pennsylvania Railroad. With black and white photos throughout and detailed diagrams specifically designed to help the scale modeler. Also includes a reprint of a 1946 article from "Railway Mechanical Engineer" magazine about the PRR's Q2s. Includes PRR roster of Q1s and Q2s. 88 pages.