Book excerpt: Diesel, the most significant development in railway technology during the 20th century, was refined and perfected resulting in locomotives that were more powerful, faster, more reliable, and more versatile than the earliest machines on the market. General Motors' Electro-Motive Division rapidly moved to become the leader in diesel-electric technology. Its business practice and models essentially defined the design and operation of diesel locomotives in North America. Producing roughly 1500 hp, Electro-Motive's famous 16-cylinder 567 diesel electric engine is at the heart of all GP7vGP20s. This book is an authoritative and richly illustrated account of EMD's General Purpose models GP7vGP20. It details these early road switchers' place in history with over 200 photos, most in color. Author Brian Solomon, contributor to numerous railway periodicals and author of over two dozen books on railway subjects, including the best-selling Specialty Press title EMD F-Unit Locomotives, shares his knowledge of the history and specifications of EMD's early road switchers. A must-read for all train enthusiasts, this book details everything from the Geep's awesome powerplant to its construction, as well as its place in railway history.