For local service, the PRR needed a locomotive with great tractive effort and fast acceleration, as there were many grades. In order to be able to prevent double heading with locomotives with two driving axles, a locomotive with three driving axles was required. The choice fell on a ten-wheeler, i.e. on the wheel arrangement 4-6-0. The boiler could be taken from the class E-6s Atlantic and the class H-10s Consolidation.
The mass balancing was designed as good as possible and moving parts were constructed as light as possible without sacrificing strength. Despite a wheel diameter of only 68 inches, a top speed of 70 mph could be approved.
The Altoona workshops made 90 locomotives for the PRR and 31 identical ones for the Long Island Railroad. The locomotives apparently fulfilled their purpose, since they achieved the required acceleration performance and could easily keep to the timetables. Despite this, it was reported that they had insufficient running smoothness and a high consumption of coal and water. However, they remained in service as long as there was steam service on the PRR.