One of the two locomotives on the Helotes Switching Company layout is the RS-27.
The ALCO RS-27 (specification DL-640) is a diesel-electric locomotive built by ALCO between December 1959 and October 1962. Only 27 examples were manufactured. With ALCO’s introduction of the Century Series line, the C-424 (specification DL-640A) replaced the RS-27 in the builder’s catalog. Today, the Minnesota Commercial Railway has the only two RS-27s left in existence, both operational. Four of the original demonstrators (#’s 640-2 through 640-5) were purchased by the UP in September 1961 and numbered 675-678. They were retired by the UP in 1971.
There is an older review of this MTH engine in the 2002 issue of Classic Toy Trains.