A "dummy" is an engine with no actual firebox, that is, no way to replenish the steam once it's used up. Dummys are supplied with steam from a central location, and are typically used in the yards only, so that, when the pressure gets low, they can scuttle back to the steam generator and restock. No one would use a dummy for actual cross-country use.

Another small engine is the tank engine (of Thomas fame). These have fireboxes and a small hopper of fuel, but no real tenders, so their range is limited.

Many people do not realize that railroad engine tenders provide water as well as coal to the engine, so that the engine's range is extended considerably.

And I'm surprised in the lyric by the "C.D.& Q," since I thought it was the "C.B. & Q.," meaning, I always thought, Council Bluffs and Quincy, a railroad whose old, rusty, seldom-used tracks ran a few blocks from my house, and whose ties I walked on many a day and night, going to either my friend's house or to the Riverview Amusement Park, in Des Moines, IA.

Bob Clayton