Pennsylvania Railroad class T1

No. 6110, the "sister" prototype of class T1 prototype No. 6111. Its streamlined casing was designed by renowned industrial designer Raymond Loewy.

A T1 prototype leaving Chicago's Union Station in February 1943 with the Manhattan Limited to New York

Before the T1, the last production express passenger engine the PRR had produced was the K4s of 1914, produced until 1928. Two experimental enlarged K5 locomotives were produced in 1929, but they weren't considered enough of an improvement to be worthwhile. After that, the PRR's attention switched to electrification and the production of electric locomotives; apparently, the railroad decided that it did not need more steam locomotives.

However, the deficiencies of the K4s became more evident during the 1930s. The locomotives performed well, but as train lengths increased they proved to be underpowered; double headed K4s locomotives became the norm on many trains. The railroad had many locomotives available, but paying two crews on two locomotives per train was expensive. Meanwhile, other railroads were leaping ahead, developing increasingly-powerful passenger train locomotives. Rival New York Central built 4-6-4 Hudsons, while other roads developed passenger 4-8-2 "Mountain" type and then 4-8-4 "Northern" type designs. The PRR's steam power began to look outdated.

The PRR began to develop steam locomotives again in the mid-to-late 1930s, but with a difference. Where previous PRR locomotive policy had been conservative, new radical designs took hold. Designers from the Baldwin Locomotive Works, the PRR's longtime development partner, were eager to prove the viability of steam in the face of new competition from Diesel-electric locomotives. They persuaded the railroad to adopt Baldwin's latest idea: the duplex locomotive. This split the locomotive's driving wheels into two sets, each with its own pair of cylinders and rods. Until then, the only locomotives with two sets of drivers were articulated locomotives, but the duplex used one rigid frame. In a duplex design cylinders could be smaller, and the weight of side and main rods could be drastically reduced. Given that the movement of the main rod could not be fully balanced, the duplex design would reduce the "hammer blow" on the track. The lower reciprocating mass meant that higher speeds could be achieved. Use of poppet valves also increased the speed because they gave very accurately timed delivery of steam to the cylinders. However, there was a drawback of the metallurgy used; the poppet valve could not withstand the stress of sustained high-speed operation (meaning over 100 mph (160 km/h) on production T1s).

The first PRR duplex was the single experimental S1 No. 6100 of 1939. It managed to reach 100.97 miles per hour (162.50 km/h) on level track while pulling a 1,350 ton passenger train. Its performance encouraged the PRR to continue to develop duplex steam locomotives. The S1 was built unnecessarily-large for her exhibition at the 1939 New York World's Fair until October 1940; therefore, its turning radius prohibited it from operating over most of the PRR network. The 6-4-4-6 design reduced driving set traction to the point that it was especially prone to wheel slip; thus only one Class S1 was built. The PRR returned to Baldwin to develop a duplex design fit for series production. The PRR ordered two Baldwin prototypes (Nos.  6110 and 6111) at a cost of $600,000 on June 26, 1940.[10] Both prototypes had numerous teething problems and were prone to wheelslip if not handled carefully by the engineer. But favorable test reports resulted in a production order for 50 T1s, split between the PRR's own Altoona Works and Baldwin. On Dec 20, 1944, the PRR Board authorized the purchase of 50 Class T1 locomotives for $14,125,000 ($282,500 per unit, equal to $4,696,229 each today). Baldwin's chief designer, Ralph P. Johnson, was responsible for the mechanical aspects of the new T1 class.[1] Designer Raymond Loewy obtained US Patent D 136,260 for an early T1 conceptual design with a high-mounted cab located over the forward driving set.[11] While that suited Baldwin's objective of making the most distinctive steam locomotive possible, practical considerations led the T1 design to be revised to the conventional cab position with a slight modification of the unique nose design included in Loewy's patent.

The last production T1 (no. 5549) entered service on August 27, 1946.[12] Engine no. 5539 developed 5,012 hp (3,737 kW), as tested between September 11, 1946, and September 14, 1946, by Chesapeake and Ohio Railway dynamometer car DM-1 while on loan to C&O. In 1944 no. 6110, tested on the stationary test plant in Altoona, developed 6,550 ihp (4,880 kW) in the cylinders at 85 mph (137 km/h).[13] They also regularly racked up over 8,000 miles a month.[14]

Due to their complexity relative to other steam locomotive designs, the T1s were difficult to maintain. Designed to run reliably at speeds of up to 100 mph (160 km/h), the T1s were so powerful that they could easily exceed their designed load and speed limitations, which in turn caused increased wear and tear, particularly to the 100-mph-limited poppet valves. They were described as "free steaming," meaning they could generally maintain boiler pressure regardless of throttle setting. They were so powerful that violent wheel slip could occur over a wide speed range if the engineer did not handle the throttle carefully; loss of driver traction at high speeds, especially when the T1 was under heavy load while ascending grades, caused damage to the poppet valves. The Franklin Type A valve gear applied to the T1s was designed for continuous speeds at 100 mph, and sprints up to 125 mph. In interviews with historian William L. Withuhn in the 1970s, Franklin engineers Julius Kirchhof and Ray Delano both claimed a Franklin technician charged with determining the cause of frequent poppet valve failures on the T1s saw them operated at speeds of up to 135-142mph to make up time with short trains of six or seven cars, determining the speed by timing when the train passed mileposts.[15]

When the PRR Board decided to dieselize all first-class prime trains in 1948, most T1s were downgraded to haul secondary trains. Some of them were withdrawn from passenger service in 1949; all were out of service by 1952. They were scrapped between 1951 and 1956.

In 2014, a non-profit group known as The T1 Trust began constructing an all-new, fully-operational T1 using the original plans with subtle performance improvements where necessary.[3] The T1 Trust's goal is to provide mainline excursion service and to set the world speed record for a steam locomotive – currently held by the LNER Class A4 No. 4468 Mallard at 126 mph.[16][17] The T1 Trust's cost estimate to build T1 number 5550 is $10 million, with an expected completion date of 2030[3] (This total has since been reduced to a bit more than $7 million, as a used PRR long haul tender has been acquired in lieu of new construction).

The construction of 5550 is also following construction and financing methods pioneered by the LNER Peppercorn Class A1 60163 Tornado project.[18] The first piece of the locomotive, the keystone-shaped number plate, was cast in April, 2014, followed by the first minor component, a driving spring link pin, in October, 2014. Major components completed as of March, 2019 include two Boxpok drivers, the prow, cab, third-course boiler and fire door. Front tube sheet construction was under way by a fabricator in St. Louis, Missouri.[19]

• A computer-generated version of a T1 was seen in the 2004 film Lemony Snicket's A Series of Unfortunate Events.[20]

• South Australian Railways 520 class, an Australian locomotive with similar streamlining style.
• LNER Peppercorn Class A1

• Staufer, Alvin F. (1962). Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900-1957 (1st ed.). Standard Print & Publishing. LCCN 62-20878.
• Reed, Brian (June 1972). Loco Profile 24: Pennsylvania Duplexii. Profile Publications.

Wikimedia Commons has media related to Pennsylvania Railroad T1.

• Chesapeake & Ohio Tests the PRR T1 - Chesapeake and Ohio Historical Magazine, May 2005 by Stephenson, David R - The C&O test report contains information that is not widely known, and some of it contradicts generally accepted beliefs about the T1.
• Photos of PRR 4-4-4-4 locomotives
• An N Scale PRR T1 4-4-4-4 scratch building project
• A group that intends to build a full-size PRR T1
• YouTube video displaying the operation of T1's on the Pennsylvania Railroad - At 3 minutes and 15 seconds, an example of the T1's infamous wheel slip can be observed.