Union Pacific 844 “The only steam locomotive never retired”, is how road number 844 of the Union Pacific Railroad (UP) was accurately described, because it was actually the only steam locomotive of a large American railroad company, which was never taken out of service. This unit built as a "Northern" type was built in 1944 as the last steam locomotive for the UP and was used until 1959. Then it was initially kept in reserve as an operational unit and was to be scrapped along with the other UP steam locomotives. Yet, as early as 1960, those responsible at UP recognized the promotionally positive advantages of special steam runs and kept it in operational condition. It thereby formed the basis of the UP steam locomotives for special services, which were increased with the "Challenger", road number 3985, in 1981 as well as the "Big Boy", road number 4014, in 2019. The UP bought 20 coal-fired, powerful 4-8-4 general-purpose steam locomotives in a two-cylinder design for the first time in 1937 from ALCO for heavy express and freight train service. They still had 1,955.8 mm / 77" driving wheels (UP road numbers 800-819). Two more series followed in 1939 (UP road numbers 820-834) as well as 1944 (UP road numbers 835-844), now with 2,032 mm / 80" driving wheels and even heavier in construction. The maximum permissible speed was set at 90 mph (145 km/h), whereby the running gear was designed for 100 mph (161 km/h). This was a special design with lightweight construction of the driving and coupled wheels of the "Boxpok" type. The last series was even equipped with two blast pipes (double smoke stacks) to improve performance. The performance data was impressive: boiler pressure of 20.7 bar / 300.23 pounds per square inch; grate area of 9.3 square meters / 100.1 square feet, heating area of 399 square meters / 4,294.8 square feet, superheater area of 130.1 square meters / 1,400.4 square feet. The weight of the locomotive and tender 411.9 metric tons, tractive effort 283.8 kilonewton / 63,801 pound-force, and a performance of 4,938 horsepower. A remarkable thing about the two last series was the large seven-axle tender, the "Centipede" design with a leading truck and five wheelsets behind it mounted rigidly in the frame. Conceived as a countermeasure to the competition from diesel locomotives, it was planned to enable long locomotive runs. With full supplies (25 metric tons of oil and 88,971 liters / 23,503.6 gallons of water), it weighed almost as much as the locomotive itself. Due to the nuisance of gas and smoke to the locomotive crews, these units were equipped in 1946 with smoke deflectors similar to the German "Wagner" design and they were converted to oil firing not least because of the coal miners' strike. Up into the second half of the Forties, these locomotives could be seen pulling prestigious UP express trains such as the "Overland Limited", "Los Angeles Limited", "Portland Rose", and "Challenger". During these runs, record-setting speeds were reportedly reached: Road number 841 pulled 25 heavy Pullman cars across Nebraska and reached maximum speeds between 105 and 112 mph (169-180 km/h). There was a report of another unit reaching the 130 mph mark (209 km/h). In their glory days, the class 800 locomotives racked up to 15,000 miles per month (24,100 km). Yet, in their last decade, they had to be content with freight trains until the last units were finally retired in 1962.