The Pennsylvania's Class K-4s Pacific No. 945, leading a double-headed limited, pauses at Chicago's Englewood Union Station in 1941. The K-4 was the Pennsylvania's standard locomotive for all types of passenger service, including high-speed mainline limiteds; when these grew too long for a single locomotive they were often double-headed. No. 945 was one of 111 engines the PRR's Altoona shops constructed in 1918. This image, which came from a Flickr site that was taken offline in 2008, appears here in order to highlight the disc driver — a rarity among PRR 4-6-2s — on the center axle. The same image appears in the ABPR Archive, having been contributed by Bud Laws.