PRR No. 3750 was built in 1918 by the Pennsylvania Railroad in Altoona. It was originally designated as a K4 until superheated, hence the change to K4s. No. 3750 remained in service with the PRR until steam was withdrawn from the railroad in 1957. No. 3750 was spared from being scrapped because, when the Pennsylvania Railroad was considering steam engines for preservation, the first K4, No. 1737, had deteriorated to the point that it was not worth preserving. The Pennsylvania decided to scrap No. 1737 and use No. 3750 as a stand-in. The locomotive was loaned to the Museum by Penn Central in 1969 and finally donated in December of 1979. It resumed its original number after restoration in 1983. Both No. 3750 and PRR No. 1361 (located at the Altoona Railroader's Museum) were designated official state steam locomotives on December 18th, 1987.