When it came to switchers, here called “shifters”, the PRR stuck to locomotives with a maximum of three axles, but still sufficient tractive power until the mid-20s. The most successful class here was the B6, of which a total of 372 were built between 1902 and 1920. It started with 79 of the basic B6, which were operated with saturated steam and had the Belpaire firebox typical of the PRR.
B6sb No. 1670 at the Railroad Museum of Pennsylvania, Strasburg
James St. John / Pennsylvania Railroad # 1670 steam locomotive (0-6-0) 1 
From 1913 onwards, 55 B6sa followed, which had a round firebox and were factory-built with a superheater. The largest number was reached by the B6sb with 238, which again had a Belpaire firebox. The B6 were also later rebuilt with superheaters and referred to as B6s. Today there are still two B6sa and B6sb, both of which are not operational. 