In the 1920's, the Southern Pacific had a need for powerful locomotives, but found that the new articulated 2-8-8-2's did not work well for them. They were a hazard to the crews when traveling through the long tunnels and snow sheds on their system. The exhaust fumes were capable of blinding and suffocating crew members, so to resolve this problem, the Southern Pacific decided to run in reverse. The next articulated engines from Baldwin were built with the cabs in the forward position. The SP went on to build many classes of these "Cab-Forwards". Broadway Limited Imports has modeled classes AC4 and AC5. Models are available in black and also with the gray boiler. The AC4 and AC5 models are identical in detail. Broadway Limited has modeled these Cab-Forwards before, but these are the first ones available with BLI's state-of-the-art Paragon3 with Rolling Thunder sound and control system.