The PRR U class engines

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This is a complete list of the 4-8-4 steam locomotives the PRR built from 1932 to 1946. They were labelled the U series, and many were used in fast freight and branch lines. Among their crews, each subclass had a different nickname.

General History:
As the 1930s drew up, the Pennsylvania Railroad began to see the deficiencies its pre-existing motive power had become apparent. Train often had to be doubleheaded, or even triple headed. The S1 duplex was not able to go much on the PRR. So, the PRR got a new mechanical engineer, an Italian immigrant named Agusto Bianchi. Bianchi analyzed the issue, then, he made his big conclusion announced at the PRR headquarters in Philadelphia. He declared that it was not only time to begin operating bigger and stronger engines, but it was time of make them fast. Hence the development of the P series Hudsons (called Keystones by the PRR), U series Berkshires, R series Northerns, and even a proposed Texas type of their own design, as opposed to based off the C&O T1. Plus numerous articulateds similar to those of subsidiary Norfolk and Western. 

Classes and their histories:

• The U1: The first 2-8-4 steam engines. These were built in the 1930s when the PRR wanted a larger engine than their L1 Mikados to haul heavier trains. The result was to simply extend the L1's trailing truck to allow for more weight distribution. They however worked alongside the I1s decapods. They were mainly referred to as "Elephants", similar to how the I1s before were called "Hippos"
• The U2: After the C&O's T1 Texas type was tested, leading to the conception of the J1, the PRR decided to do similar tests with other C&O engines. These included a Kanawha 2-8-4, a Greenbrier 4-8-4, a Hudson, and one of the new Lima type 4-8-6s. In the end, the PRR decided to use the Kanawha and the Greenbrier to create a pair of new, strong engines. The U2 and the R5 were the results of these ideas. The U2 mainly became a fast freight engine, but was mostly used on freight through all of the PRR. The U2 engines were mainly referred to as "Juniatas", after the Mountain Range.
• The U3: lastly, the J1 Texas was shortened and got a belpaire firebox, these were called "Super Juniatas." They were most prominent on coal trains handed over from the Norfolk and Western, a prominent subsidiary of the PRR, which was later absorbed into the company in 1967 (then later became part when the PRR and Southern merged to form the AU Penn Southern).