The EMD DDA40X was a 6,600 traction hp (4.9 MW) D-D diesel locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois for the Union Pacific Railroad. Forty seven locomotives of this type were built between June 1969 and September 1971, and numbered from UP 6900 to UP 6946.
The first locomotive, UP 6900, was delivered in time to participate in the celebrations of the centennial anniversary of the completion of the transcontinental railroad by driving a golden spike at Promontory Summit, Utah. The class was therefore named Centennial by the Union Pacific.
The DDA40X is 98 ft 5 in (30 m) long, and is the longest diesel locomotive ever built. The frames were fabricated by an outside contractor, the John Mohr Company of Chicago, since the locomotive frame length exceeded the abilities of EMD's plant. It remains the most powerful American diesel locomotive type ever built and is one of the most powerful in the world, exceeded only by the Soviet multi-unit designs such as the most powerful of them, the 4TE10S, which on other hand should be competed with the similar ones, for instance the largest and most powerful such locomotive (set), the 8-unit A-B-B-B-B-B-B-A EMD F7. A 4-unit DDA40X lash-up was common for the 1973-1975 period. The DDA40X comprises two diesel engines, each providing 3,300 traction hp. Although the most powerful American diesel locomotive ever built, it was far from the only dual engine locomotive built. The EMD E-series was one of the more popular dual-engine locomotives, and other manufacturers had produced locomotives utilizing up to 4 diesel engines. Baldwin Locomotive Works (BLW) produced a prototype that was to contain 8 V8 diesel engines but it never went into production.
The 'X' in the designation stood for Experimental. The DDA40X locomotives were used as the testbeds for technology that would go into future EMD products. The modular electronic control systems later used on EMD's Dash-2 line of locomotives were first used on the DDA40X. The locomotive was the first to be able to load-test itself using its dynamic braking resistors as an electrical load so that external equipment was not required. The DDA40X used the wide-nosed cab from the FP45 cowl units. This design closely resembled the Canadian comfort cab used on nearly all hood unit diesel locomotives today, but predated it by two decades.
As the DDA40X program was deemed a testbed, a number of experiments were conducted during the service life of these locomotives. One such test included fitting a few of the units with air raid sirens in order to warn trackside personnel when away from grade crossings. These tests were inconclusive.
Source: Wikipedia (http://en.wikipedia.org/wiki/DD40X)
Warning: This model is no longer available. It will be replaced for a new version for RW3 in October.