The PRR T1, also know as the 4-4-4-4 Duplex was perhaps one of the fastest steam engines ever developed. They were nicknamed Sharks with their nose design. They look fast even when sitting still. They where made to run and that they did. Their top speed was 120MPH and some unconfirmed reports have them pushing 140MPH. They could run Chicago to Harrisburg without having to stop for coal or water.
But they where flawed, at slow speeds their second driver would slipped uncontrollably until the engineer could get a hold of it. PRR, in its over zealous pride tried to develop an engine at the end of the steam era that would trump proven designed locomotives, specifically the 4-8-4 Northern.
Ultimately it is this engine that started the Pennsy down the road to ruin. It took nearly 20 years but their pride eventually got the better of them. Worse yet, to save the company they merged with their arch rival and formed Penn Central. That was a disaster from the start.
Either way, it is a sharp locomotive.