With the development of the new Type 244 engine, ALCO introduced the PA passenger locomotive in addition to the FA freight locomotive in 1946. Not only did the propulsion electrics come from General Electric, the streamlined and modern design of the car body also came from Ray Patten, head of GE's design department. The PA got the more powerful sixteen-cylinder engine and stood on two bogies with the A1A wheel arrangement. What all PA and FA have in common is that black smoke came out when accelerating due to the lack of air in the turbo lag.

With a 2,000 hp engine, 169 PA1 and 39 PB1 without a cab were built. From 1950 onwards, 81 PA2 and eight PB2 were built with 2,250 hp. Three PA-2s went to Brazil with a gauge of 5 ft 3 in. Some railroads also used their PA and PB in freight traffic, but the number of units remained behind EMD's E series due to lower reliability. The Massachusetts Bay Transit Authority used its locomotives until the late 1970s and then sold them to the Ferrocarriles Nacionales de México, which continued to use them until 1981.