The class Q1 was a 2-6-4T tank locomotive designed for commuter traffic between Reading Terminal in Philadelphia and Chestnut Hill. It had needed three sets of drivers for heavy grades, but also had to be flexible for sharp curves. A Wootten firebox was added to burn anthacite. Since fast turnarounds were needed at Philadelphia Terminal, the P&R opted for a tank locomotive design to dispense with the need to turn the locomotive. A total of ten locomotives were numbered 376 to 385.

The first six Q1-a were built in 1903 by Baldwin. Four more Q1-b followed in the following year which were a little heavier and had a larger coal supply, but were otherwise identical. Eight were rebuilt between 1920 and 1922 and designated Q1-c. Their boiler had lost 47 tubes, possibly to improve water circulation in the space between the tubes. Another rebuild in 1924 made them Q1-d. In this rebuild, the weight distribution had been changed to decrease the weight on the drivers. They were scrapped between 1930 and 1936, after the lines where they operated had been electrified.