The Pennsylvania Railroad's T1 4-4-4-4 duplex drive locomotive has become a legend, for due to the advance of dieselization it had a brief service life. The first two (Nos. 6110-6111) were designed and built by Baldwin Locomotive Works in 1942, and the remaining 50 were erected in 1946 by the Pennsylvania's own Altoona Shops (Nos. 5500-5524) or by Baldwin (Nos. 5525-5549). The striking "shark nose" styling was by famed designer Raymond Loewy, and was emulated not only by Baldwin's "shark nose" diesels but by a group of 4-8-4s built for the South Australian Railways. The T1 was originally built with a more streamlined front end having three side "port­holes" (see the following photo of No. 5526), but all or most were later modified with access steps from the pilot to the catwalk as shown here.

The T1 class had 80-inch drivers and four 19¾x26-inch cylinders, and sustained 300 pounds per square inch of boiler pressure. (Nine locomotives later had their cylinder diameter reduced to 18¾x26.) They had a grate area of 92 square feet, 4209 square feet of evaporative heating surface, and 1430 square feet of superheating surface. The T1 developed 58,300 pounds of tractive effort. No. 5527, a Baldwin product, poses above at an unknown location (probably Englewood Station, Chicago), in a photo of indeterminate origin.