Prototype. The Southern Pacific had used Cab-Forward locomotives since the early 1900s on its mountain routes. With the smokestack located behind the cab, the engine crew wasn’t asphyxiated during the run, which included miles of tunnels and snowsheds.
To help deal with increased rail traffic during World War II, the War Production Board approved the SP’s order for 20 new 4-8-8-2 Cab-Forward locomotives. Baldwin delivered the locomotives, classified as AC-12 by the SP, in 1943 and 1944. For more history on Cab-Forward locomotives, see Cab-Forward: The Story of Southern Pacific Articulated Locomotives by Robert J. Church.
The dimensions of the model match drawings in The Model Railroader Cyclopedia, Vol. 1: Steam Locomotives.
Appearance. InterMountain did an excellent job modeling the AC-12 in HO scale. The locomotive and tender are made primarily of plastic. Separately applied parts include all handrails and piping, whistle, and dynamo. The tender also has separately applied underbody brake rigging.
The cab interior has a boiler backhead with painted gauges and valves.
The locomotive and tender lettering are straight and match prototype photos.
The model has an articulated frame. As on the prototype, the model’s front engine is rigid and the rear engine is hinged at the front.
A wiring harness connects the electronics in the locomotive to the DCC decoder and speaker in the tender.
Before operating the locomotive I thoroughly lubricated it with plastic-safe light oil as indicated in the instruction manual. All the running gear operated smoothly without any binding.
I tested the model in DC with an MRC Tech 4 power pack and in DCC with an MRC Prodigy Advance that delivers 14.5 VAC to the track. In both DC and DCC speed tests the AC-12 accelerated to a top speed of 40 scale mph. This is slower than the prototype, which could reach more than 60 mph.
I also ran the model with a 20-car train along our layout for 15 minutes without problems. The model looked great rounding a 32″ curve and traveled forward through no. 6 turnouts without any difficulty. However, the locomotive’s trailing truck tended to derail when backing through turnouts.
Sound effects. In DC the model’s sounds and lights came on at 5 volts. As I advanced the throttle, the exhaust sounds started before the model began moving. These sounds were not synchronized to the motion of the drivers.
The sound system operated more appropriately on a DCC layout. At rest automatic sounds included the characteristic air pumps. The chuffing exhaust sounds were synchronized to the motion of the drivers. User-triggered functions include the bell, whistle, coupler, and a water stop sequence. The many programmable configuration variables (CVs) are outlined in an extensive instruction manual on CD-ROM.
The InterMountain AC-12 is a great-looking model. I hope the DC sound and top speed issues will be addressed in future releases of the Cab-Forward.
Price: $439.95 (DCC sound), $329.95 (DC no sound)
Manufacturer
InterMountain Railway Co.
30 E 9th Ave.
Longmont, CO 80504
www.imrcmodels.com
Paint schemes: all Southern Pacific in multiple road numbers, versions with or without “Southern Pacific” tender lettering available.
Era: 1943 to late 1950s
Features:
Electrical pickup on 16 drivers and 12 tender wheels
Front and rear Kadee Magne-Matic operating couplers at correct height
Illuminated headlight, backup light, and number boards
Metal RP-25 contour wheels, in gauge
Minimum radius: 24″
SoundTraxx Tsunami DCC sound decoder (DCC versions only)
Weight: 2 pounds 1 ounce (engine weighs 1 pound 11 ounces)
The detail on these is nearly identical to the prototype I saw in the Sacramento RR museum. They are museum quality. I bought 2. 40mph suits me fine. They are gorgeous. I have DC power pack and a BLI DCC controller. They are beautiful just to look at. I have never run them on a layout.