The “Pennsylvania” of the Philadelphia & Reading wasn't only the biggest of the camelbacks designed by James Milhlolland, but also the biggest locomotive in the world when it was completed in 1863. It was a 0-12-0 that was used as pusher on the steep Falls Grade near Philadelphia, Pennsylvania.

A special feature of this locomotive was that it didn't have a separate tender, but wasn't a real tank locomotive either. This meant that it had no coal bunker and only small water tanks, but was stoked before each of the short climbs. Since it was found out that the freight cars of the time couldn't handle the forces of this massive locomotive, it was rebuilt in 1870. It now had only five axles, a tender and a new cab.

Since the Philadelphia & Reading had access to anthracite culm as cheap fuel, switchers were also built as Camelbacks with Wootten fireboxes. This included the class A-4, which had a 0-4-0 wheel arrangement and was built a total of 19 times in 1902 and 1903. They were modernized between 1905 and 1907 with higher boiler pressure and a larger tender.

Only number 1187 has survived, which was sold to the E&G Brooke Iron Company in 1946 and was in use there until 1962. It was now purchased by the Strasburg Railroad and was used there on short runs in front of passenger trains. However, since the locomotive did not produce enough steam for line service, it was retired in 1967. In 2020 it was purchased by the Age of Steam Roundhouse and is being cosmetically restored there.

One of the Philadelphia & Reading inspection engines was number 100, built by Baldwin in 1902. It originally had a 4-4-0 wheel arrangement and a narrow boiler. The boiler was deeply embedded in the passenger compartment and there were four armchairs on each of its sides. In 1913 it was rebuilt with the wheel arrangement 4-4-2, although it was technically almost a new vehicle. As a result, it had larger driving wheels, larger cylinders and a new boiler. This was also long and small in diameter, but now also had a flat Wootten firebox. It was now able to pull two passenger cars without any problems and was in use until 1929.

Superintendent L.B. Paxson of the Philadelphia & Reading was convinced in the mid-1890s that an express locomotive with one powered axle would still be sufficient to haul express trains at high speed. He was thinking in particular of some trains between Jersey City and Philadelphia that covered the 90 miles with a light load. When asked about the ideal wheel arrangement, the choice fell on 4-2-2, which was popular in Great Britain and was called “Single” or “Bicycle” in the US.

A Wootten firebox with a grate of 75 square feet was installed in order to be able to produce a lot of steam at high speeds with the combustion of residues from the anthracite processing. This meant that it was designed as a Camelback locomotive with the cab in the middle of the boiler. The steam dome sat behind the cab on the firebox. The power was provided by a four-cylinder compound engine of the Vauclain type, in which a jointly cast high and low pressure cylinder were present on each side.

After the number 385 built in 1895, the almost identical number 378 followed in the following year. The locomotives ran the mentioned line including the intermediate stops at an average of 51.4 mph and ran very smoothly. The 385 is said to have even reached 120 mph for a short time what is disputable. Even though the two locomotives easily hauled trains of around 350 tons, the low adhesive weight was soon no longer sufficient.

Both were rebuilt in 1904 into locomotives with a 4-4-0 wheel arrangement, which differed from each other. One thing they had in common, however, was that both received a simple two-cylinder engine with 19 by 26-inch cylinders. The 385 became the class D10-a and retained its 84.25 inch driver diameter. It lost its combustion chamber during the rebuild and instead had a larger tube heating surface. The 378, now class D10-b, had the drivers reduced to 78.5 inches and still had a combustion chamber, but also had a slightly larger boiler overall.

Since the Reading Company was not allowed to build new locomotive types during World War II due to the War Production Board's regulations, existing locomotives had to be rebuilt. The class T-1 was created by rebuilding a total of 30 class I-10sa Consolidations to the 4-8-4 wheel arrangement. Among other things, the boiler with Wootten firebox were taken over and enlarged.

The first 20 locomotives were intended only for freight service and only had roller bearings on the carrying axles. Only in the last ten were roller bearings used on all axles in order to be suitable for possible use in front of passenger trains. In fact, they were rarely used in passenger service, but mostly in front of fast freight trains.

Their regular use initially ended in 1954. However, as traffic volumes increased, Reading used some of these machines again and also rented nine to the PRR. After these operations ended in 1957, the Reading ran a series of special trips with four locomotives that lasted until 1964 and became known as the "Iron Horse Rambles". The four locomotives used for this are all preserved today, of which only 2102 is operational.