Introduced: 1987 (discontinued mid-1990's)
This model is a bit of a Frankenstein's monster, and definitely the odd stepchild in the Atlas Alco pantheon. It uses the same shell as the 1986 Atlas/Kato RS-11, the original 1983 Atlas/Kato RS-3 chassis/mechanism, the 3-axle trucks from the 1987 Atlas/Kato RSD-4/5, and (for a change of pace) its very own new fuel tank.
Features include a split-frame metal chassis, split-frame metal truck assemblies, blackened wheels, all-wheel drive (no traction tires), and all-wheel pick-up. The motor is an open-sided 5-poler. All gearing is plastic. Directional lighting is provided by PC boards mounted on either end of the chassis. The couplers are truck-mounted Rapidos (open pilots). Wheels are low-profile and have no problems on Code-55 track. No flywheels, though (those wouldn't show up on an Atlas/Kato model until their 1988 RS-1).
Although the RSD-12 has the same shell and chassis as the Atlas/Kato RS-11, the "guts" of the two mechanisms are quite different. Apparantly the redesigned RS-11 mechanism was a bit of a disappointment, so Kato decided to revert back to the original RS-3 internals for this model (RSD-12 above, RS-11 motor below) -
Performance on these models is most excellent. They run smoothly and quietly at all throttle levels. Pickup is flawless, slow-speed creep is superb, and pulling power is impressive. The top-end speed is a bit high, but that's a minor nitpick. And running characteristics aside, these things just flat-out look great (especially as compared to other 1980's diesel models).
I'm told that the shell dimensions on these RSD-12 models were fudged a bit (vis'a'vis the prototype) in order to accommodate the old RS-3 chassis. Unfortunately, given Atlas's newfound commitment to prototypical accuracy (coupled with the fact that very few roads actually used RSD-12's), it seems unlikely that a new (and more accurate) "Atlas Classic" RSD-12 will ever see the light of day (given the fact that it would require completely new tooling).
Many of these RSD-12's come in boxes labeled "Special Limited Edition". Atlas tells me that these "special" runs were limited to a single road name/number.
Removing the shell requires a bit of patience and a gentle hand (IE, leave the elbow grease at home). I use a small screwdriver to pry the shell away from the chassis a little bit at a time (starting at one end and working my way around). Eventually it'll slide up and off.