I’ll have to find a picture, but what kind of locomotive is the full length but half the height of your typical diesel locomotive?
Probably a “slug” locomotive, which is essentially the diesel-electric locomotive without the diesel part or the cab: Slug (railroad) - Wikipedia A lot of times these are literally just old locomotives with the top half cut off!
The other options I was thinking (depending on where you saw it) would be mabye a mining locomotive (which can be pretty short squat little things, but nowhere near the size of a full-size mainline loco), or some switchers are fairly squat so the operator can see 360 degrees.
Yup, sounds like a slug to me.
It could also be a Green Goat which is a hybrid type switcher locomotive. It uses a small generator to charge a bank of batteries that drive the traction motors that drive the wheels. Here’s a better picture.
How this differs from a slug is that a slug does not operate on its own, it has to get its electrical energy from an attached diesel electric locomotive. It that case, the diesel engine powers the traction motors of its own loco plus the slug. The slug can’t generate its own power. The benefit is that you have more wheels through which to apply power, which is useful when starting a train from a standing stop.
So, if it was operating by itself, it was a green goat. If it was in tandem with another full size loco, then it was probably a slug.
Did it look like this?
Agreed with Greasy Jack. Sounds like a slug.