"Advances in valve gear and the application of limited cutoff improved steam admission and thus improved engine efficiency while helping reduce cylinder back pressure (which retarded piston thrust), allowing engines to work faster. Advances to boiler design and the introduction of the four-wheel radial trailing truck introduced a whole new breed of locomotives capable of supplying large volumes of steam over sustained periods, and this changed the ways that railroads bought and assigned mainline motive power." As Mr. Solomon notes, the 1930s was the last great decade of locomotive's advancement. During this time further mechanical and operational improvements were made such as roller-bearings and counterbalancing to reduce wear, while ever larger boilers increased horsepower and tonnage ratings.
The most powerful ever put into service rolled out of Lima, Alco, and Baldwin during the 1930s and early 1940s such as the 4-6-6-4 "Challengers," 4-8-8-4 "Big Boys" (built exclusively for Union Pacific), 2-8-8-4 "Yellowstones," and the 2-6-6-6 "Alleghenies" put to use on the Virginian and Chesapeake & Ohio. In addition, there was the incredible machines built by the Norfolk & Western. Arguably, this coal-hauling juggernaut built better locomotives than the "Big Three" manufacturers with such models as the 4-8-4 J's, 2-6-6-4 A's, and 2-8-8-2 Y's. While the book does not touch on the subject there were several railroads such as the N&W, Milwaukee Road, Illinois Central, Pennsylvania, and others that were quite skilled in the area of steam technology, producing their very own locomotives (such as the Pennsy's "Duplex Drive" locomotives, mentioned in the book).
The middle chapters highlight single-engine locomotives under a rigid frame, featuring six, eight, and ten-driver models. As the early 20th century progressed locomotives became ever-larger. However, as advancements and refinements improved wheel arrangements became specialized. For instance, the 4-6-2 "Pacific" developed into the quintessential passenger locomotive handling daily assignments while the 2-8-2 "Mikado" and 4-8-2 "Mountain" could often be found powering freight trains. As larger models were unveiled in the 1930s, largely due to heavier trains, the 4-8-2 and 4-8-4 "Northern" were often assigned to passenger consists while those railroads which purchased or built articulated/Mallet locomotives utilized them in heavy freight service (the 10-drivered locomotive was never terribly popular but designs like the 2-10-2 and 2-10-4 could be found in freight service).
The book's final chapter, Titans Of The Rails, focuses exclusively on the large, articulated locomotives. While entire books could, and have, been written on each type Mr. Solomon does a fine job of providing a general overview here. Of the roads which employed these monsters many found the 2-8-8-2 and 4-6-6-4 most practical although there was a varying degree of arrangements. Perhaps the most fascinating was the "Cab Forward" employed by Southern Pacific. This design was basically an inverted locomotive and kept smoke clear of train crews traveling through the many snow sheds and tunnels over California's Donner Pass. If you enjoy big steam, The Majesty Of Big Steam, is a great title to have in your collection.