Dear N Scale Modelers, Bachmann announced a future release of DD40AX in Union Pacific. Here are the details:

Photo by Craig Walker

The EMD DDA40X was a 6,600 hp (4.9 MW) D-D diesel locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois, for the Union Pacific Railroad. 47 locomotives were built between June 1969 and September 1971; they were numbered UP #6900–6946.

The first locomotive, #6900, was delivered in time to participate in the celebrations of the 100th 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 the longest diesel locomotive design ever built, at 98 ft 5 in (30 m). The locomotive frame length required exceeded the abilities of EMD's plant, so the frames were fabricated by an outside contractor, the John Mohr Company of Chicago. Even today, it is the most powerful diesel locomotive type ever built, although it achieves this by using two diesel prime movers.

The 'X' in the designation stood for Experimental: the DDA40X locomotives were the testbeds for much technology that would go into future EMD products. They pioneered the modular electronic control systems later used on EMD's Dash-2 line of locomotives. For the first time, the locomotive was 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 diesels 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, however.

Source Wikipedia