Perhaps the best-known 4-6-2's of all time was Pennsylvania Railroad's K-4s class. These steamers carried a simple beauty to it, which also lent to much of its success. However, beneath its good looks these 4-6-2s could also perform quite exceptionally.. Another reason for the K-4s' popularity, at least among railfans and historians, was that fact that most were built the Pennsylvania's own Juanita shops, which built well over 300 in total with the remaining manufactured by Baldwin. It is important to point out, however, that the K-4s was not the only Pacific class the Pennsy owned; the railroad actually rostered over a half-dozen different types built over a 20-year span and virtually all (save for one) were listed as Class K.
The K-4s is widely recognized today for its ruggedness and reliability; sporting PRR's noteworthy Belpaire fireboxes they could be found anywhere and everywhere on the railroad's massive system. The Pennsy was also one of the few roads to operate the wheel arrangement in freight service. Generally, the Pacific type was a passenger locomotive but some roads did choose to expand its range. Today, two of the PRR's legendary 4-6-2s are preserved.
By the turn of the 20th century many of the larger railroads realized that they were running into a problem; passenger trains were becoming larger and heavier as demand steadily increased which was resulting in multiple units needed to keep these expedited consists on a strict schedule. In 1902 the Chesapeake & Ohio was the first to put the 4-6-2 design into regular service for the very reasons mentioned above. Somewhat surprisingly, it was not until 1906 that the Pennsylvania Railroad began looking at the possibility of utilizing such a locomotive for passenger operations. In 1907 the PRR collaborated with the American Locomotive Company's (Alco) Pittsburgh Works to build an experimental Pacific.
Interestingly, even here the railroad was still quite slow, deliberate, and calculated in its approach with the new locomotive. This first 4-6-2 was given road number 7067 and listed as Class K-28; it featured 80-inch drivers, a tractive effort of nearly 33,000 pounds, and weighed more than 208 tons (including tender). For an early Pacific design it was quite heavy in comparison to the C&O's examples (by more than 53 tons) with a tractive effort slightly better. This would be the only 4-6-2 of this class and it was later super-heated and designated as Class K-28s before being scrapped in 1933. In any event, the PRR was quite pleased with its trials and decided on the Pacific as its primary power for passenger service.
The K-4s was actually the fifth of six different classes of 4-6-2's the railroad owned following (by date) the K-28, K-2sa, K-21s/VK-1, K-29, and K3s. What would eventually become the PRR Class K-4s Pacifics resulted from an earlier Class E-6 Atlantic design, incorporating the 4-4-2 wheel arrangement, and the American Locomotive Company’s K-29 Pacific design. Mechanically the most famous features of the K-4s' would be their Belpaire fireboxes, 80-inch drivers, and Walschaerts valve gear, which blended just the right amount of power and speed to haul virtually anything the PRR asked of them. The PRR's designation for its K-4s was as follows: the "K" denoted the railroad's fleet of Pacifics while the "4" was simply the class number of the wheel arrangement; lastly, the "s" referred to the class being superheated.
The K-4s locomotives were first constructed between 1910 and 1911 and they proved so successful that while most of the railroad's 4-6-2s were retired by the 1930s they would soldier on until all steam was retired from the property in the late 1950s. Most of the 450 K-4s units were built directly by the railroad's own Juniata, Pennsylvania shop forces (375) while Baldwin also chipped in with 75 examples. Interestingly, while versatile and able to pull serious tonnage the K-4s was not Pennsy's most powerful Pacific, which was the K-5 built in 1929 that by far had the highest tractive effort, boiler pressure, and overall weight of any 4-6-2 the railroad operated. Despite their power, however, the K-5 was not considered successful on the PRR. Below is a quick snapshot of the K-4s.
Incredibly, while hundreds of 4-6-2s were put into service just two survived the scrappers torch, #1361 current at the Railroaders Memorial Museum in Altoona and #3750 at the Railroad Museum of Pennsylvania. For years #1361 sat as a moment at the railroad's fabled Horseshoe Curve in Pennsylvania after being retired by the railroad in 1957. In 1986 the locomotive was removed from its static display and restored to operational status to pull excursions. After a lengthy rebuild beginning in the late 1990s by the Horseshoe Curve Chapter of the NRHS where millions of dollars had been spent without an operable locomotive it was decided to put the restoration on hold due to rising costs and return the Pacific to public display.