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Description
The Pennsylvania Railroad was the most enthusiastic user of duplex locomotives in the United States, as it needed more powerful steam locomotives but wanted to reduce the size and weight of the cylinders as well as the "hammer blow" on the track, but the locomotives had short lives due to their complexity and their debut shortly before dieselization. Its most common duplex was the T1 4-4-4-4 express passenger engine, of which Baldwin and Altoona built 52, all with Raymond Loewy's streamlined casing. Allegedly, they were the world's fastest steam locomotives, but that remains insufficiently substantiated. All 52 were scrapped, so if you want to see a T1 operating, either visit a miniature railway or wait for the enthusiasts to finish building No. 5550. A less successful duplex was the unique experimental prototype Q1 4-6-4-4 dual-service engine, which was also styled by Raymond Loewy but had the casing removed to simplify maintenance during World War II. It was extremely powerful and pulled a 125-car train weighing 10,000 tons during a test, but its rear cylinders were cramped and overheated due to being mounted by the firebox, and its long steam pipesIts successor, the Q2 4-4-6-4 freight engine, was more successful with 26 engines built, and set a record of 7987 horsepower during a static test, but the whole class was also scrapped early in the transition era. Models of a T1 and the Q1 are displayed together at the Railroad Museum of Pennsylvania in Strasburg.

Description
The Pennsylvania Railroad was the most enthusiastic user of duplex locomotives in the United States, as it needed more powerful steam locomotives but wanted to reduce the size and weight of the cylinders as well as the "hammer blow" on the track, but the locomotives had short lives due to their complexity and their debut shortly before dieselization. Its most common duplex was the T1 4-4-4-4 express passenger engine, of which Baldwin and Altoona built 52, all with Raymond Loewy's streamlined casing. Allegedly, they were the world's fastest steam locomotives, but that remains insufficiently substantiated. All 52 were scrapped, so if you want to see a T1 operating, either visit a miniature railway or wait for the enthusiasts to finish building No. 5550. A less successful duplex was the unique experimental prototype Q1 4-6-4-4 dual-service engine, which was also styled by Raymond Loewy but had the casing removed to simplify maintenance during World War II. It was extremely powerful and pulled a 125-car train weighing 10,000 tons during a test, but its rear cylinders were cramped and overheated due to being mounted by the firebox, and its long steam pipesIts successor, the Q2 4-4-6-4 freight engine, was more successful with 26 engines built, and set a record of 7987 horsepower during a static test, but the whole class was also scrapped early in the transition era. Models of a T1 and the Q1 are displayed together at the Railroad Museum of Pennsylvania in Strasburg.