The Pennsylvania Railroad of TTL
1927: the PRR hires a Milanese Mechanical Engineer namedas Augusto Lombardi. Having seen the NYC Hudsons, they desire bigger and better engines, albeit still with interchangeable parts, which they require Lombardi to use on his first designs.
1928: Lombardi designs the U1 2-8-4, based on the I1. And the R2 4-8-4, based on the M1. Both are moderate successes. But are not built in quantity like other PRR steamers of the time. For this reason of the lack of interchangeable parts, Lombardi is given permission to make entirely new designs.
1929: Lombardi introduces a new method of locomotive numbering due to numbering system having once been random. The process dictates a letter for the motive power type (S for steam, E for electric, etc.), the class of the engine (L, K, M, I, etc.), and the engine’s number. For instance, L1 Mikado 520 would be referred to as “SL-520.” and K4 Pacific 1361 would be “SK-1361"
1930: After a few years, Lombardi announce that he will work with Baldwin and Lima to develop his next big project. A larger engine to replace the K4 Pacific in fast Passenger runs.
1933: SR-7100, the first R3 4-8-4, rolls out of Altoona. 300 would be originally built with the intent of replacing the K4 Pacific. However, they would instead supplement them often and end up on mixed traffic later in life.
1935: The first U2 2-8-4, SU-7400 rolls out of Altoona. The railroad envisions these engines to compliment the L1 Mikados and M1 Mountains in fast freight. With I1s and U1s roll on heavier, slower trains.
Late 30s: Lombardi builds the R3s and U2s in massive numbers. Unlike the past PRR engines, they have fewer interchangeable parts. but are still loved by crews and the PRR.
1938: The electrification of the NE Corridor is completed. Though some engines continue to venture as far as Harrisburg.
1940: Many prominent members of the Norfolk and Western brass begin replacing their PRR counterparts in preparation for merger. Which doesn't happen until 1978. Most significantly, William J. Jenks, president of the N&W, becomes a key advisor of Martin W. Clement
1942: The PRR introduces the first two T1 duplexes. Along with them, they also build some streamlined 4-8-4s called R4s to serve as backup.
1945: The PRR builds the J1, T1, and Q2 engines.
1946-1950: The PRR begins modifying their facilities to be like those of is subsidiary Norfolk and Western. Allowing for a more efficient maintenance process than before. In addition, several more N&W J class steamers are built for use on the Pennsy. Under which they becomes the R5 class of engines. As such, engine like 611 or the fictional 622 become SR-611.
1957: The first K4, 1737, is retired and put on display at Northumberland, PA.
1957-1963: Most of the K4 Pacifics are retired. The good news is that among the ones preserved in this timeline are 5399 (my personal favorite of the class), 3768 (with rebuilt shrouding), 1120 (also with rebuilt shrouding), and 3847. Plus many more K4 Pacifics. Which become to Americans what the Black Five is to British enthusiasts.
1965: All PRR steam engines smaller than the M1 Mountains are retired. This includes the L1 Mikados, H series Consolidations, among others. Only the I1 2-10-0s and several switchers remain by 1976.
1966: The R2, U1, Q2, and T1 are all retired. Thankfully, several are preserved of each class.
1967: The PRR introduces the Keystone Limited, which supplements the Broadway Limited as a NY-Chicago train, albeit one running via the Panhandle Line through Columbus, OH and Logansport, IN.
1970: The PRR Historical Society gets together to plan restoration of several PRR engines. The L1 Mikados and J1 Texas types are retired with some examples preserved of each. At this point, the M1, I1, U2, and R3 are the only steamers left in regular service.
1978: The N&W is fully absorbed into the PRR, while the Abingdon and Blacksburg branch lines, which still ran the M class 4-8-0s, become tourist lines. The Huckleberry Scenic and the Virginia Creeper Scenic. Both continue running with 4-8-0s, though the former also buys a pair of ATSF diesels.
1980: The PRR finally ends steam. The last fantrip being R3 7236 and I1 1753 on a double header from Harrisburg to Chicago via Ft. Wayne and return. Many remaining engines are sent to museums. Subsidiary Norfolk and western dieselizes soon after, also saving more off their engines than in OTL. That said, many of the modernized steam facilities are kept around. If only for show in the yards, though return to use for steam excursions.
1981: Their first engine, E6 460 goes to work at the Strasburg railroad. N&W 611 is also restored for the Southern Excursion Program.
1982: R3 7236 is sent to the Southern's Birmingham shops for restoration.
1983: The PRR begins using battery operated electric locomotives for most duties. As their maitenance is slightly less time consuming than those of diesels. As well as maitenance facilities able to be smaller.
1984: T1 Duplex 5536 is slated for possible restoration. Which takes place 1989.
1987: K4s 1361 is restored, as is 3750. N&W 1218 is also restored for the Southern excursion service.
1980s-early 90s: Many surviving K4s are restored for excursions on short lines or the mainline. Notably 5399, which notably uses her a original tender as her water car. Not to mention the fact the modernized Pacific is located in Ft. Wayne, IN. With NKP Berkshire 765.
1996: To celebrate its sesquicentennial, the PRR operates several steam excursions with engines from both the PRR and N&W. Numerous restored K4s take part. As do T1 5536, R3 7236, I1 1753, M1 6755, and a few more. all operate at varying points. N&W 611 and 1218 also escape retirement from excursions following the SOU steam program’s end by joining this program.
1997-present: The PRR continues hosting several excursions with both N&W and PRR engines. While most of their passenger train lines are upgraded to be on par with the high speed NE Corridor. These lines now host speeds up to 100 mph.