The Pennsylvania Railroad's class A1 was a class of 0-4-0 type steam locomotives.
History
The Pennsylvania Railroad's class A1 was a class of 0-4-0 switcher type steam locomotive. Built from 1886 to 1892, when the A1 was introduced into service, 0-4-0s were being used by other railroads. In time the 0-6-0 came and other railroads neglected the 0-4-0. But, on the Pennsylvania Railroad, this wasn't happening. This is because, the PRR had a bunch of tight trackage and street trackage as well. The Pennsylvania Railroad elected to use a small locomotive to operate these tight and confined tracks. By the 1920s the Pennsylvania Railroad class A1 was greatly replaced by the even larger class A5s, the largest 0-4-0s on the Pennsylvania Railroad's roster of 0-4-0s in service at the time. By the 1950s as the diesel switchers became available for easier and more efficient switching duties, the Pennsylvania Railroad started to replace the 0-4-0s and 0-6-0s notably the Pennsylvania Railroad class B6sb switchers with diesel switchers. In 1957, as with all Pennsylvania Railroad steam locomotives still in service, they were completely replaced by the diesel locomotive.