Research Train Question

What is the 2nd unit that is on most Research trains. I saw one go past a few months back, and it had a brown, almost switcher type B-unit that was tagged on. The 2nd, unit had no number. The train was small, just a Geep, the Brown one, and the business car.

Perhaps that was not an engine.........maybe a track geometry car? (I have never seen one, but.....)

Looked like an SW1200 Calf. Do not know....

The brown unit behind the loco is some form of geometry unit which I think is made from an SD35. I have seen this train a few times but I have not gotten close enough to get a real good look at the middle unit. From what I have seen, the middle unit is a six axle unit like some kind of slug.

Yes, sir. However, I believe the unit I saw was a 4 axle. Cannot remember...