The GG1, one of the PRR's most famous and recognizable locomotives, is also one of the most curiously designed. Technically two locomotives under one shell (a "G" class locomotive is a 4-6-0 by PRR specification, therefore the GG1 was two "G" locomotives in a 4-6-0:0-6-4 arrangement). This added up to a 4.6k horsepower locomotive that was staggeringly powerful, even by today's standards. Designed in the 20's, built in 30's, and not retired until the 80's, the GG1 had an incredible lifespan (even when they were cut in two and run as GG½'s) and survives today as a testament to its time in both its unique Loewy-design and overwhelming performance.
Amtrak and Penn Central: Thanks to the long life and usefulness of the GG1, many outlived the PRR, finding themselves in Penn Central, and later in their life, Amtrak paint. These locomotives were used in everything from freight service to pulling Amtrak Passenger trains.