The Pennsylvania Railroad adopted a classification scheme for its locomotives early on. Initially, each locomotive type was identified by a letter of the alphabet, starting with Class A and working through the letters. Only standardized types were classified in this way; non-standard, inherited locomotives were just classed as 'odd' and their wheel arrangement, e.g. 'odd 4-4-0'. The limitations of this scheme became obvious as soon as the railroad passed twenty classes of standardized locomotive.
So, a new scheme was adopted, which would classify the railroad's steam locomotives until the end of steam operation in 1957. Each locomotive wheel arrangement was assigned a capital letter, and then a subsequent number identified the individual type of locomotive within that overall classification. Subsequent lower-case letters identified variations too small to qualify as a different locomotive class, generally again counting from 'a' upwards. A lower case 's' immediately following the number stood for a superheated locomotive.
Experimental and acquired locomotives were normally given higher numbers, in the 20s and 30s.
Electric locomotives were mostly classified under the steam locomotive classification system, and are therefore included. Those that were not (the E2 and E3 experimental locomotives, and the E44), and diesel locomotives, are not currently included here; diesel locomotives had several PRR classifications but all are better known by the classifications given by their builders.
The classes were as follows:
Supplanted in regular shifter (PRR parlance for switcher) duty by larger locomotives early in the Twentieth century, 0-4-0 types continued to be used on tightly curved trackage in industrial districts where a larger locomotive could not go.
- A1: This tank locomotive class was formerly class Q; 8 were built between 1886 and 1892. The driving wheels were 44" diameter.
- A2: These were also formerly class Q. 31 were built 1885-1892; equipped with 50" drivers. There were also 8 Class A2a tank locomotives.
- A3: Formerly class U; 81 were built at Altoona between 1887-1891. Equipped with the PRR's trademark Belpaire firebox. Some converted to Class A3a tank locomotives, some surviving into the 1930s in this form.
- A4: 64 of these were built at Altoona, 1906-1913. The drivers were 50" and a Belpaire firebox was used.
- A5s: 47 of these were built at Altoona, 1916-1924. Belpaire firebox, piston valves, Walschaerts valve gear. Possibly the last 0-4-0 locomotives built for a major American railroad, and used on trackage that could not take a locomotive with a longer wheelbase.
- A21: ex-Vandalia class VA1. 4 built by Pittsburgh Locomotive Works, 1880-1883. 50" drivers.
- A22: ex-Vandalia class VA2. 19 built at Terre Haute shops, 1883-1893.
- A22a: One converted A22 with saddle tank, no tender.
- A23: ex-Vandalia class VA3. 2 blt by Pittsburgh Locomotive Works, 1893
- A29: One (#7109) built at Fort Wayne, 1879. 48" drivers.
- A30: One built at Columbus shops, 1897. 50" drivers. No tender.
The Pennsylvania Railroad kept the 0-6-0 as its preferred shifter type until the end of steam; the larger 0-8-0, much favored by other railroads, never really took off on the Pennsy. This was partly because the PRR commonly used road locomotives, such as Consolidations (2-8-0s) and Decapods (2-10-0s), for heavier switching duties.
- B1: Tank locomotive: formerly class F. 24 built at Altoona 1869-1873. 44" drivers.
- B1: The B1 classification was re-used for the PRR's only class of electric switchers. 42 of them were built between 1926 and 1935.
- B2: Formerly class H. 53 built by the Pennsy between 1872-1883. 44" drivers.
- B3: 211 of these were built by the PRR between 1882 and 1892. They were formerly class M. Drivers were 50" and they had an Altoona firebox. Also, the B3a saddle tank conversion.
- B4: This was formerly under Class M also. 36 were built in Altoona in 1892. They had 50" drivers and a Belpaire firebox. There was also a class B4a that had a larger grate area but was otherwise similar; 97 of these were built between 1893 and 1904.
- B5: These were converted from Class H1 Consolidations by removing the last pair of driving wheels and the pilot truck. 57 were converted as class B5 and 32 as B5a with minor differences.
- B6: The B6 and its subsequent revisions were the most common 0-6-0 locomotives on the PRR in the Twentieth century. 52 were built as plain Class B6 between 1902-1913, and most of those were subsequently superheated as class B6s. The original B6 had a Belpaire firebox, but the next revision, the B6sa, had a radial stay firebox instead. 55 of these were built; they also had Walschearts valve gear instead of Stephenson valve gear on the earlier locomotives. The final revision, the B6sb, reverted to the Belpaire firebox and was the most successful; 238 of these were built from 1916-1926.
- B7: 32 converted from Class H3a Consolidations by removing last pair of driving wheels and the pilot truck; 7 B7b were produced from class H3b, also.
- B8: 267 of these were built for Lines West, who preferred their own design to the PRR standard B6.
- B21: Ex Vandalia class VB1; 4 locomotives.
- B22: Ex Vandalia class VB2; 13 locomotives.
- B23: Ex Vandalia class VB3; 13 locomotives.
- B28s: PRR's USRA 0-6-0s. 30 were recieved 1918-1919.
- B29: 136 built by Alco and Lima 1903-1913; equipped with Radial-stay fireboxes, slide valves, and Stephenson valve gear.
- B30: ex-TWV&O. 2 built by Rome Locomotive Works, 1890.
- B31: ex-TC&OR. 2 built by Rogers between 1891-1892. 50" drivers.
- B32: ex-TC&OR. 1 built by Baldwin, 1892. 50" drivers.
- B33: ex-CL&N. 1 built by Pittsburgh 1901. 50" drivers.
- B35: 11 built 1885-1888. 50" drivers.
- B61: ex-CA&C. Two engines. 48" drivers.
The PRR never really accepted the 0-8-0, preferring to use Consolidations and Decapods in the heavier switching roles. They produced only one major type new, though a few others were conversions from Consolidations.
- C1: 90 of these giants among 0-8-0s were built in 1925 and 1927, for heavy switching and transfer duties. They were not altogether popular with crews, for their rough ride and propensity for mechanical troubles, and tended to be the first laid aside during traffic slumps. These were larger than many road locomotives.
- C29: 10 engines, converted from classes H1, H2 and H2a by removing the pilot truck.
- C30: Solitary example #8434 was built from new as a tank locomotive by Columbus Shops in 1895.
- C31: Solitary example #8542 was converted from a Consolidation built for the Elk Mountain Railway, absorbed into the PRR; it was also made into a side tank locomotive at that time.
The premier passenger locomotive type until late in the Ninteenth Century, the 4-4-0 was supplanted by more powerful types and ended its days in suburban and branch line service.
- D1: Formerly class A; 13 were built at Altoona between 1868-1872. 68" drivers.
- D2: These were formerly class B. 20 were built at Altoona between 1869-1880. 62" drivers. Class D2a also, 45 built at Altoona between 1881-1882. 68" drivers.
- D3: These were formerly class B as well. 67 built at Altoona between 1869-1881. 62" drivers.
- D4: Built with a large grate for anthracite fuel, and formerly PRR Class C, 37 mountain-climbing 62" driving wheel examples were built at Altoona between 1873 and 1880, of which 15 were later given 68" wheels and classed D4a.
- D5: These were formerly class G, and had small 56" drivers. Eighteen were built at Altoona between 1870 and 1873.
- D6: These graceful, high-drivered locomotives (78") were formerly class K and were built at Altoona between 1881 and 1883; nineteen in total were constructed.
- D7: Formerly Class A, these were anthracite burners with large grates. 58 68" wheeled examples and 61 62" wheeled D7a locomotives were built between 1883-1891 at Altoona.
- D8: 45 of these locomotives, formerly class N, were built by the PRR between 1883-1888. 62" drivers. Class D8a was formerly class O and there were 86 of them; the differences were minor.
- D9: These were also formerly class O; 4 of the plain D9 with 62" wheels and 13 of the D9a with 68" wheels were built by the PRR in 1889.
- D10: Again, formerly class O; 51 small-wheeled and 58 large-wheeled were built in 1889-1892.
- D11: These were formerly class P, and again there were small and large wheeled (D11a) variants; 21 and 65 respectively were built 1883-1888.
- D12: Also formerly class P, 2 small and 41 large-wheeled examples were built.
- D13: These introduced a fatter 57" boiler compared to the 54" of previous locomotives. Again, 2 small and 77 large wheeled built 1892/3.
- D14: Classes D14 (6) and D14a (16) were both high-drivered (68" and 80" respectively).
- D15: Only one D15 was built; it was a Lindner cross compound with high drivers; it featured a British-style footplate and splashers.
- D16: Classes D16 and D16a were the familiar small drivered/big drivered pair (68" vs. 80"), 76 and 73 built respectively; class D16b was an improved small-drivered version of which 262 were built, while D16c and D16d were improved large-drivered ones (12 and 45 built). Later, 241 examples of all subtypes were rebuilt with piston valves and superheat as class D16sb, with 68" drivers, for suburban service. Three lasted until after the Second World War, and one of those, #1223, retained its passenger slatted pilot, this one was preserved, and is still in existence; it was, until relatively recently, in running order.
- E1: Three of these camelbacks, with Wooten fireboxes, were built in 1899. In addition, one E1a with a radial-stay firebox was built.
- E2: 82 of these modern (for the time) Atlantics were built 1901/2. They had radial stay fireboxes, slide valves, and Stephenson valve gear. They were followed by the E2a which had a Belpaire firebox; 93 of these were built 1902-5. Production of the E2b version followed; these had inboard piston valves, and 70 were built, both by the PRR themselves and by Alco. Classification E2c covered Alco-built slide valve equipped locomotives, of which there were 22; while 32 class E2d were built by the PRR in Altoona with conventional piston valves and Walschearts valve gear.
- E3: 178 of these Atlantics in various sub-classes were built; unlike the E2s, many were superheated later on.
- E5: 12 of these were built, and all were later superheated; they were identical to later E3 locomotives but for the use of a Kiesel cast steel trailing truck instead of the fabricated truck formerly used.
- E6s:Called the "Apex of the Atlantics", these were some of the last 4-4-2 locomotives produced in the United States. They were Atlantics more powerful than many Pacifics, and excellent flatland racers. 83 were built 1912-1914 and some survived to the end of steam.
- E7s: These were rebuilds from class E2 and its subclasses, given superheating and piston valves. Radial stay E2 locomotives became E7sa.
- E21: ex-Vandalia class VE1. 4 built by Alco at Schenectady in 1902. 20-1/2" x 26" cylinders, 79" drivers.
- E22: ex-Vandalia class VE2. 5 built by Alco at Schenectady in 1903. 21" x 26" cylinders, 79" drivers.
- E23: ex-Vandalia class VE3. 10 built by Alco at Schenectady between 1906-1910. 21-1/2" x 26" cylinders, 79" drivers. radial stay firebox, inboard piston valves, Stephenson valve gear.
On the Pennsy, Moguls were fast freight locomotives. They were the first major type to die out, with none surviving into the 1930s
The Ten-Wheeler was a natural progression of the 4-4-0 type, extended with an extra pair of driving wheels. They were superseded in express passenger service by locomotives such as the Atlantic and Pacific equipped with a trailing truck and wider fireboxes, and in freight service by the Consolidation. The type enjoyed a comeback with the G5s for suburban service.
- G1: Formerly the class D, 286 of these were built between 1868 and 1875. The drivers were 56". Class G1a had 50" drivers, converted from G1.
- G2: These were formerly class E; 195 were built between 1869 and 1884. The drivers were 50".
- G3: Formerly class X; 21 were built at the Fort Wayne shops. They had 68" drivers.
- G4: 38 of these were built at Altoona between 1899-1901 with 72" drivers, and 75 G4a with 62" drivers.
- G5s: 90 of these Kiesel-designed suburban passenger locomotives were built between 1923 and 1925. 68" drivers, piston valves, Walschearts valve gear, Belpaire firebox. 30 of that number were for the Long Island Rail Road.
- G21: ex-Vandalia class VG1. 4 were built by Pittsburgh in 1886. 50" drivers.
- G22: ex-Vandalia class VG2. 4 were built by Pittsburgh in 1889. 50" drivers.
- G23: ex-Vandalia class VG3. 3 were built by Schenectady in 1891. 57" drivers.
- G24: ex-Vandalia class VG4. 7 were built Pittsburgh between 1892-1893. 51" drivers.
- G25: ex-Vandalia class VG5. 1 was built by Pittsburgh in 1892. 72" drivers.
- G25a: ex-Vandalia class VG5a. 2 were built by Pittsburgh in 1892. 72" drivers.
- G25b: ex-Vandalia class VG5b. 1 was built by Pittsburgh in 1893. 72" drivers.
- G26a: ex-Vandalia class VG6a. 2 were built by Pittsburgh in 1895. 56" drivers.
- G30: ex-TWV&O. 5 were built by Rogers between 1891-1892. 56" drivers.
- G31: ex-TWV&O. 8 were built by Baldwin in 1892. 56" drivers.
- G32: ex-C&M. 2 were built by Rogers in 1892. 55" drivers.
- G33: ex-C&M. 1 were built by Rogers in 1893. 54" drivers.
- G34: ex-Grand Rapids & Indiana Rail Way class GG4. 6 were built by Baldwin between 1899-1900. 62" drivers.
- G35: ex-GR&I class GG5s. 3 were built by Pittsburgh in 1901. 62" drivers.
- G35a: ex-GR&I class GG5s. 3 were built by Pittsburgh 1901. 62" drivers.
- G35sa: ex-GR&I class GG5sa. 3 were built by Pittsburgh in 1902. 62" drivers.
- G36s: ex-GR&I class GG6s. 2 were built by Alco in 1907 and 1909. 68" drivers.
- G37s: ex-GR&I class GG7s. 6 were built by Alco 1907 and 1909. 68" drivers.
- G61: ex-CA&C. 7 were built by Rogers in 1889-1891. 54" drivers.
- G61a: ex-CA&C. 1 was built by Rogers in 1890. 54" drivers.
- H1: Originally class I; 545 were built between 1875 and 1886. Altoona firebox.
- H2: 105 H2 and 105 H2a were built from 1886 to 1890.
- H3: Formerly class R, 418 of these locomotives were built between 1885 and 1892. The first PRR class to have the road's trademark Belpaire firebox. Followed by 329 class H3a with boiler pressure raised to 150 psi, then 143 H3b. One H3 still survives.
- H4: A Lines West design;105 built 1897-1901.
- H5: Huge and heavy for its time; fifteen were built in the Juniata Shops in 1898 as pushers for the Gallitzin grade.
- H6: A Lines East design produced in huge quantities. The original H6 (189 built) had a narrow firebox between the frames, but the H6a modification had a broad firebox straddling the rear drivers. 1242 of them were produced. The H6b had piston valves and Walschearts valve gear; 603 of this version were built. Some, modified with superheaters and other modern features, survived into the late 1940s.
- H8: The H8 was a whole new generation; much bigger, much more powerful. A large number of variants of the H8, and the subsequent H9 and H10, were built, but the total production of all three classes was 1206. They served until the end of steam. The H8/9/10, the E6s and the G5s were sister locomotives in that their boilers were practically identical, and their overall dimensions were very similar.
- H9: The H9 had one-inch larger diameter cylinders than the H8, but otherwise was identical. The boiler on the H8 had proven so able a steam generator that larger cylinders could be installed, providing greater tractive effort and power, and still not over-tax the boiler at higher speeds.
- H10: The H10 was again a further one-inch increase in cylinder diameter from the H9; even the H9's cylinders didn't overtax the boiler, and the PRR repeated the process of expanding the cylinders.
- H28: Alco-built experimental locomotive, in many ways a precursor to the H8.
- H30: One locomotive acquired from the Cleveland & Marietta.
- H31: 2 built in 1892 acquired from another railroad.
- H32: 10 locomotives acquired with the Grand Rapids & Indiana; their class GH2, built 1896-1898.
- H33: 12 locomotives acquired with the Grand Rapids & Indiana; their class GH3, built 1892-1893.
- H34s: 18 locomotives acquired with the Grand Rapids & Indiana; their class GH4s & GH4sa, built 1905-1910.
- H61: One locomotive acquired from the Cleveland, Akron & Columbus, built in 1888 by Baldwin.
The PRR only ever owned one class of Decapod, but that class numbered almost six hundred.
- I1s: The PRR built 123 of these mountain luggers in its own Altoona Works in 1918/9, and then placed an order with Baldwin for 475 more delivered in 1922/3, the largest locomotive order ever placed at that time with a single builder for a single class of locomotive. Most were converted to class I1sa (valve gear changes increasing the maximum cutoff). One survives in preservation.
Two experimental Prairie locomotives were received from Alco by the PRR, but the type never took hold; the Pennsy preferred the four-wheel leading truck of the Pacific instead.
No, not a mistake! Both experimental Prairies were out of service before the 1930s, so when the PRR built 125 2-10-4 locomotives in the 1940s they re-used the J classification for them.
- J1: The PRR found itself in need of modern steam freight locomotives during the Second World War, but the War Production Board forbade the development of new locomotive types. The PRR had no suitable existing designs, so it cast around for designs on other railroads that might be acceptable. In the C&O's T-1 class it found a winner. The design was 'Pennsy-ized' in detail design, but remained otherwise the same. 65 J1 and 60 J1a, differing little, were produced. They served until the end of steam.
Pacifics rapidly became a favorite type on the PRR, and the K4s Pacific was especially favored, becoming one of the most famous classes of locomotive in the world.
- K2: 153 class K2 and 72 K2a were produced in 1910-13, all but two later being superheated. They were small and straight-boilered. Some existed until nearly the end. They had high 80" drivers.
- K3s: Similar to the K2s, but for Lines West, with their distinctive tenders, superheated from construction, and they had stokers fitted.
- K4s: The most famous Pacifics in the world? 425 of these were built by the PRR and by Baldwin between 1914 and 1928. They remained largely unreplaced in front-line service until the end. Two survive in preservation.
- K5: Two experimental super-power Pacifics built in 1929. #5698 was built by the PRR with a cast-bed locomotive frame and a cast one-piece cylinder saddle similar to the one later used on the M1a. #5699 was built by Baldwin and featured Italian-designed Caprotti poppet valves.
- K21s: Twelve ex-Vandalia locomotives built 1910-13.
- K28 Experimental Pacific upon which the K2 was largely based.
- K29 Experimental Pacific, this time influencing the K4s.
The Mikado type was the freight counterpart to the Pacific, though the Pennsy's were very much overshadowed by their Decapods.
- L1s: 574 of these were bult by the PRR, Baldwin and Lima, 1914-19. They were the freight counterparts to the K4s and shared the same boiler and many other parts.
- L2s: Five USRA Light Mikados acquired when the PRR absorbed the GR&I. Smaller than the L1s.
- L5: Siderodded, jackshaft drive electric locomotives, really 2-4-4-2 in wheel arrangement. 21 were built, twenty of them DC electric, one AC. They were not notably successful.
- L6: Electric freight locomotive. Three were built; twenty-eight more were going to be built, but plans changed; GG1s displaced P5 locomotives to freight work, and the L6 was no longer needed.
Possibly the best Mountains ever? These were certainly in the running.
- M1: 201 of these mighty Mountains were built 1923 & 1926 by the PRR, Baldwin and Lima. Intended as dual service locomotives, they ended up being almost exclusively used on fast freight. 72" drivers.
In 1930 one hundred revised M1a were built; they featured one-piece cast cylinder saddles with inside steam delivery pipes, and two air compressors instead of one. Thirty-eight of these were converted to class M1b with higher-pressure boilers and firebox circulators, making them much more powerful.
On the PRR, the 2-10-2 was exclusively a Lines West design, and used for drag freights.
- N1s: 35 of these were built by Alco and 25 by Baldwin to a PRR Lines West design. They had huge, swollen looking boilers and were very impressive locomotives.
- N2s: These were USRA Heavy 2-10-2 locomotives built by both Alco and Baldwin. They were smaller and lighter looking than the N1s; again, used exclusively on Lines West. All of them were eventually given new boilers with the PRR trademark Belpaire firebox and became class N2sa.
This classification was used exclusively by six experimental electric locomotives.
- O1: Six experimental electric locomotives. Successful, but underpowered, and generally worked in pairs. They were the precursor to the P5.
Again, exclusively electric locomotives - and don't even
breathe the word 'Hudson' around PRR men.
- P5: Intended to be the express passenger locomotive for the new PRR Electrification, the P5 was envisaged as an 'electric K4s', but bidirectional, thus both leading and trailing trucks were 4-wheel. 64 boxcab locomotives were produced between 1931 and 1933. The box cab design proved to provide insufficient crew collision protection, and the P5a was redesigned with a center cab and streamlined lines; 28 were produced like this. Just like the K4s they proved inadequate singly for the latest heavy express trains, and when a larger replacement was found, the P5 locomotives were regeared for freight work.
The Pennsy's freight Duplexes were, really the 4-10-4s the United States never built -- and they might have been more unequivocally successful had they been built as conventional 4-10-4s instead. Be that as it may, they were the most stupendously powerful rigid-framed locomotives ever built.
- Q1: One Q1 was built in 1943. Bizarrely for an intended freighter, it was semi-streamlined and had large, 77" drivers. It was not highly successful.
- Q2: The Pennsy's second effort at a freight Duplex was much more successful. On the test plant at Altoona, the Q2 was measured at the highest power output ever measured in static test, almost eight thousand horsepower. 26 were built in 1944-5. They were out of service in 1949, after the Pennsy had decided to dieselize, doomed by much higher maintenance costs than simpler, older locomotives.
The PRR never acquired any steam 4-8-4s, but it did build one electric locomotive to this plan.
- R1: The solitary R1 was built as a rigid-framed alternative to the prototype GG1. Though good, the GG1 was marginally better and was selected for volume production. The R1 stayed in service, however.
Two quite different experimental express passenger locomotives.
- S1: The first Duplex locomotive the PRR ever built. More of a show locomotive than a serious attempt at producing a practical locomotive to produce in volume, the S1 was too long and with too great an overhang to fit on much of the system, and it ended up, after spending several years on display at the New York World's Fair, hauling trains on the long, straight raceway between Chicago and Crestline, Ohio. Stupendously powerful and fast, the S1 could have broken records.
- S2: The Pennsy's experiment with steam turbine technology, the S1 featured a Westinghouse turbine geared directly to the wheels. Although effective at high speeds, the S2 proved less able to deal with low-speed operation, proving highly uneconomic. Possibly the only locomotive ever to have four stacks.
The intended successor to the mighty K4s.
- T1 Two prototypes were built in 1942 and fifty production locomotives followed in 1946. Fast and powerful when they worked right; expensive and difficult to maintain, though, and prone to violent wheelslip, they proved a step too far. All were sidelined by 1949/50.
Articulated locomotives were classified by considering them two locomotives joined back-to-back:
0-8-8-0 locomotives were generally used in slow speed roles; heavy switchers, transfer switchers, and pushers. The PRR's were no different.
- HC1s: One built by the PRR at Altoona Works in 1919 for road service. Proved to be wrongly proportioned and badly designed; its failure turned the PRR off from articulated locomotives for good.
- HH1: During World War 2 the PRR was desperately short of motive power, and it leaned on the Norfolk and Western, of which the PRR owned 40%, to give some locomotives. All the N&W had to spare were six 1919-vintage USRA 2-8-8-2 locomotives, N&W class Y-3. They served until about 1947.
- HH1s: One locomotive built by Alco in 1911.
- DD1: The DD1 consisted of two 4-4-0 third rail electric locomotives semi-permanently coupled back to back. They were built for the Hudson tunnels and the electrified Penn Station and the vast complex of Sunnyside yard. DD1s hauled all locomotive-hauled trains from Penn Station to Manhattan Transfer where steam locomotives took over. After the electrification was extended to Washington, D.C. and Harrisburg, Pennsylvania, the DD1s continued in service for local switching and transfer service. Thirty-three pairs were produced between 1909 and 1911.
- DD2:The DD2 was intended as the new freight locomotive required if the Pennsy's electrification was extended past Harrisburg, Pennsylvania to Pittsburgh or further. One prototype was produced in 1938, but the extension of the electrification never happened, and the DD2 was destined to be a solitary example. It looked like a shortened GG1.
- HH1: Nicknamed 'Big Liz' by PRR men, this astoundingly powerful electric locomotive was the first heavy-duty, main-line electric locomotive the PRR built. It proved, in fact, too powerful for 1917 technology; after pulling out one too many couplers it was assigned to pusher service. Even in that role it was too powerful, wrecking many freightcars by pushing just too damn hard.
- HH2: In 1956, the Great Northern shut down its electrified district, finding it unneeded now that the railroad had diesel locomotives. The PRR snapped up eight of its 1926-1929 built locomotives at bargain-basement prices, putting seven in service and using one for spares. They didn't last more than ten years in service, but for the price, they were a bargain.
- GG1: The most famous electric locomotive, ever? Only the Swiss Crocodiles might compete with the GG1 for that honor. Sleek, fast and powerful, the GG1 had it all, and 139 of them were built between 1934 and 1944. They outlasted the PRR, and the Penn Central after that, serving for almost fifty years until they finally started to wear out. A dozen or so are preserved.
Sources: Pennsy Power and Pennsy Power II by Alvin F. Staufer and North East Rails's PRR Steam Roster at http://www.northeast.railfan.net/.
Yes, I know, this writeup is enormous; so was the PRR, and I feel the enormity is fitting.