ALCO PA1/PB1 PA2/PB2
An ALCO/M-K PA-4 of theDelaware and Hudson Railroad in April 1978
Type and origin Power type Diesel-electric Builder Partnership ofAmerican Locomotive Company (ALCO) andGeneral Electric (GE) Model PA1, PB1, PA2, PB2 Build date June 1946 – December 1953 Total produced 297
Specifications Configuration: ​  • AAR A1A-A1A Gauge 4 ft 8+1⁄2 in (1,435 mm)standard gauge 1,600 mm (5 ft 3 in), Brazil Length 65 ft 8 in (20.02 m) Loco weight 306,000 lb (138,799 kg; 139 t) Fuel type Diesel Prime mover ALCO16-244G V16 Engine type V16Four-stroke diesel Aspiration Turbocharger Displacement 10,688 cu in (175.14 L) Generator DC Traction motors 4x GE 746 or 752 DC traction motors Cylinders 16 Cylinder size 9 in × 10+1⁄2 in (229 mm × 267 mm) Transmission Diesel-electric MU working Yes Loco brake Independent air. Optional:Dynamic Train brakes Air
Performance figures Maximum speed 117 mph (188 km/h) Power output 2,000 hp (1,490 kW) — PA-1/PB-1 2,250 hp (1,680 kW) — PA-2/PB-2 Tractive effort 51,000 lbf (226.86 kN)
Career Class Erie- PA1- PA-20 PA2- PA-22 NH- PA1- DER-3a NYC- PA1- various PB1- various PA2- DPA-4a PRR- PA1- AP20 P&LE- PA1- DPA-2c PA2- DPA-14b WAB- PA1- D20 Locale North America,Brazil Disposition Three preserved, one operational, one under cosmetic restoration, one converted to steam generator car, remainder scrapped.

TheALCO PA was a family ofA1A-A1Adiesel locomotives built to haulpassenger trains. The locomotives were built inSchenectady, New York, in theUnited States, by a partnership of theAmerican Locomotive Company (ALCO) andGeneral Electric (GE) between June, 1946 and December, 1953. Designed by General Electric's Ray Patten (along with theirALCO FA cousins), they were of acab unit design; both cab-equipped leadA unitPA and cabless boosterB unitPB models were built. While externally the PB models were slightly shorter than the PA model,^[1] they shared many of the same characteristics, both aesthetically and mechanically. However, they were not as reliable asEMD E-units.^[2]

ALCO's designation of P indicates that they were geared for higher speeds and passenger use, whereas the F designation marks these locomotives as being geared primarily for freight use. However, beyond this, their design was largely similar - aside from the PA/PB's both being larger A1A-A1A types with an even more striking nose - and many railroads used PA and FA locomotives for both freight and passenger service.

Although the majority of the PAs and PBs have been scrapped, six examples have survived. Four PAs are now preserved in railroad museums, while one PA has been restored to operational condition byDelaware-Lackawanna for use on excursion trains and a converted PB still remains in service as a power car.

There were two models of PAs: the 2,000 horsepower (1,500 kW)PA-1/PB-1, which was built between September 1946 and June 1950, and the 2,250 horsepower (1,680 kW)PA-2/PB-2, which was built between April, 1950 and December, 1953.^{[citation needed]}

The PAs, as well as their cousins, theALCO FAs, were born as a result of ALCO's development of a new diesel engine design, the Model 244. In early 1944, development started on the new design, and by November 1945 the first engines were beginning to undergo tests. This unusually-short testing sequence was brought about by the decision of ALCO's senior management that the engine and an associated line of road locomotives had to be introduced no later than the end of 1946.

In preparation for this deadline, by January, 1946, the first 16-cylinder 244 engines were being tested, and, while a strike delayed work on the locomotives, the first two PA units were released for road tests in June, 1946 for testing for one month on theLehigh Valley Railroad. After these first tests were completed, the locomotives returned to the factory for refurbishment and engine replacement.

In September, 1946, the first production units, an A-B-A set of PA1s inSanta Fe colors, numbered #51L, 51A and 51B, were released from the factory and sent to New York'sWaldorf-Astoria Hotel, which had a private railroad siding, for exhibition before being launched into road service.^[3] This set was repowered in August, 1954 with EMD 16-567C engines rated at 1,750 hp (1,300 kW). This EMD repowering of the PAs was economically unfeasible, and the remaining Santa Fe PAs retained their 244 engines.

Four PA-1s previously operated by the Santa Fe were sold toDelaware and Hudson Railway in 1967. In 1974-1975, they were rebuilt for the D&H asPA-4s byMorrison Knudsen and equipped with ALCO's 251 V-12 engines.^[4] Under D&H ownership, they were used by Amtrak for theAdirondack.^[5] (Amtrak itself only purchasedEMDE- andF-units fromthe railroads whose service it replaced for its diesel roster, and never owned any PAs.^[5][6]) They were used by theMassachusetts Bay Transit Authority in the late 1970s, then byFerrocarriles Nacionales de México in 1978–81.

Fans deemed the PA one of the most beautiful diesels and an "Honorary Steam Locomotive", as noted by ProfessorGeorge W. Hilton in a book review in September, 1968Trains Magazine. When accelerating, until the turbocharger came up to speed, thick clouds of black smoke would pour from the exhaust stacks due toturbo lag. Photographing a moving PA while smoking became a prime objective ofrailfans.^[7][8]

The PA-2 units sold to the1,600 mm (5 ft 3 in)broad gaugeCompanhia Paulista de Estradas de Ferro ofSão Paulo State inBrazil were equipped with a barpilot and solid horizontal steel pilot beam. One of these locomotives survives.

Five PA units and one converted PB unit survive.

• One surviving unit, #600, is from the order of three broad gauge units sold toCompanhia Paulista de Estradas de Ferro in Brazil. It exists at the Companhia Paulista Museum at Jundiai,São Paulo as a shell with no prime mover and no side panels. A restoration began in 2001 but has not been completed.^{[citation needed][needs update]}
• All fourDelaware & Hudson-operated PA-4s have survived, with two being in the United States, and the other two in Mexico.
  • From 1981 to 2000, No.16 and No.18 remained stored inEmpalme,Sonora,Mexico. In 2000, theSmithsonian Institution and rail preservationist Doyle McCormack obtained the units and brought them back to the United States.
    • No.16, which was heavily damaged in a derailment while in Mexico, was planned to be cosmetically restored into its original "Warbonnet" colors for theSmithsonian Institution. The unit was acquired by theMuseum of the American Railroad in 2011 and transported to the museum's new site in Frisco, Texas. Since then, it has been under restoration, with plans to return it to its original Warbonnet appearance and original number of ATSF 59L.^[9]
    • No.18 was owned by Doyle McCormack and has been undergoing restoration since 2002. It has been restored as Nickel Plate Road 190, a recreation of the first locomotive McCormack got to ride.^[10] The locomotive was moved to theOregon Rail Heritage Center, inPortland, Oregon in 2012, where restoration work continued to take place. In March 2023, it was announced that theGenesee Valley Transportation Company would purchase the locomotive, with plans to restore it to operation for excursion use.^[11] It arrived in Scranton, Pennsylvania in May 2023.^[12][13] In June 2025, mechanical restoration of the locomotive was complete. It made its public debut in July onDelaware-Lackawanna trackage.^[14][15][16]
  • No.17 and No.19 are preserved at the National Museum of Mexican Railways inPuebla. Unit DH-17 (former D&H #17) was painted in the classicSouthern PacificDaylight colors, but as of February 2010 had been painted over in primer.
• Ex-Denver and Rio Grande PB-1 6002 was converted to a steam generator car in October 1965; it gained Blomberg B trucks in 1980. It was sold toAnsco in late 1987 for service on theSki Train and later sold again in 2007 to theAlgoma Central Railway.

• Aslaksen, James and McCormack, Doyle.NKP190.com. Retrieved on March 26, 2005.
• Hayden, Bob, ed. (1980).Model Railroader Cyclopedia-Volume 2: Diesel Locomotives. Kalmbach Books.ISBN 0-89024-547-9.
• Hollingsworth, Brian and Arthur F. Cook (1987).The Great Book of Trains. Portland House, New York, NY.ISBN 0-517-64515-7.
• Pinkepank, Jerry A. (1973).The Second Diesel Spotter's Guide. Kalmbach Publishing Co., Milwaukee, WI.ISBN 0-89024-026-4.
• Romano, Andy (1997).PA: Alco's Glamour Girl. Four Ways West Publications.ISBN 1-885614-16-0.
• Stumpf, Rolf.ALCO World: Paulista RR. Retrieved on March 26, 2005.
• The Santa Fe Diesel Volume One: Dieselization - 1960 by Dr. Cinthia Priest pages 52–56.
• http://utahrails.net/ajkristopans/REPOWEREDLOCOMOTIVES.php see EMD order #8506 dated August 1954 for repowering data on the AT&SF 51 set of PAs.^{[better source needed]}

Wikimedia Commons has media related toALCO PA locomotives.

• America's PA projectArchived 2021-05-03 at theWayback Machine
• DH-17 and DH-19 at the National Museum of Mexican Railroads website.

• A1A-A1A locomotives
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