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7000-hp., 4-8-8-4 Type Locomotives for the Union Pacific Capacity and features of construction make these engines outstanding examples of the locomotive builder's art
The 4-8-8-4 Type locomotive, 20 of which were delivered in the fall of  1941, to the Union Pacific by the American Locomotive Company are the largest in size and heaviest from the standpoint of total engine and tender weight, of any simple articulated eight-coupled locomotives which have been built. Each locomotive weighs 762,200 lb. and the tender weighs 435,800 lb. The maximum tractive force is 135,375 lb.   Some idea of the capacity of this type of locomotive to move traffic may be gained from the fact that it is designed to develop 7000 hp. and built to operate at a maximum speed of 80 m.p.h. It is expected to deliver a high power output continuously at 70 m.p.h. This tremendous capacity enables one of these locomotives, to haul, unassisted, a mile of loaded freight at a speed of a mile a minute, on level track.   Another impressive feature is that they are precision  built, carefully constructed and balanced. As a result, no "breaking-in" period was required. In fact, a few hours after its arrival at Omaha the first locomotive delivered was attached to a train which otherwise would have been double-headed, and soon was on the way to Cheyenne, running up to a speed of 60 m.p.h.
The service to which these locomotives have been assigned consists of handling heavier capacity freight trains from Ogden, Utah to Green River, Wyoming, one of the most difficult runs in the world. Each locomotive has a sufficient capacity to haul these trains over the heaviest mountain grades in territory without double-heading.Supplementing this lateral flexibility, the system of spring suspension permits flexibility in the vertical plane. The locomotive as a whole has three point suspension.   The two engine beds are so connected that they are completely rigid in a vertical plane, all adjustment to curvature in this plane being through the spring suspension.  All axles are equipped with roller bearings and all roller bearing boxes are equipped with heat indicators. Roller bearings are also used in all bearings of the Walschaert Valve Gear.     The boiler is of enormous size in keeping with the great capacity of the locomotive and includes as part of its equipment two water glasses with a difference of 5 in. in the level of lowest indication, for operation on 1 1/2 per cent maximum grades. The lowest indications are 5 1/2 in. and 10 1/2 in. above the highest point of the crown sheet, respectively, with the locomotive standing on level tangent track.	The locomotive is the embodiment of great power and weight combined with a high degree of refinement in construction.
When the locomotives are assigned to districts where the maximum gradient is 2.2 per cent the water columns can be raised one inch on the boiler attachment so that the lowest readings become 6 1/2 in. on the crown sheet.  The front end is equipped with what is called a "Labyrinth" Spark Arrester, which is a patented device developed by Union Pacific. The advantage of this device is that the gas passages through the front of the smokebox range from 96 per cent to 112 per cent of the net gas area through the tubes and flues. The tender superstructure is carried on a wheel arrangement consisting of five pairs of wheels mounted on pedestal cast integral with the bed. A lubricator feeds oil to all tender truck boxes and to the tender truck center plate. The water capacity is 25,000 gallons, and fuel, 28 tons.   The service to which these locomotives have been assigned consists of handling heavier capacity freight trains from Ogden, Utah to Green River, Wyoming, one of the most difficult runs in the world. Each locomotive has a sufficient capacity to haul these trains over the heaviest mountain grades in territory without double-heading.