|Horseshoe Curve-1959. Here is an original photo that I took at the Pennsylvania Railroad's Horseshoe Curve near Altoona, Pennsylvania, on 03 September 1959. Shown here (R to L) are PRR engine #8668, one unit whose number is unknown, and engine #8665. All are AS-18AM's built by the American Locomotive Company in 1958 and rated at 1,800 horsepower each. They are pushing a westbound mixed-cargo freight train around the Horseshoe Curve and up the Allegheny Mountains to Gallitzin and points West. The N-5 Caboose is #477181.