Reply to Rome K/G:
Hmm, yea they must use them [dummy engines] out west in the mountain ranges. Wow! that locomotive is about 55 ton heavier than a D11. No wonder it takes four 583H sidebooms to pick em up. Those are some big turbos on those engines, I wonder if they are a high volume and lower pressure turbo for the slower running engines?
That cabless locomotive is typically called a "B Unit" meaning it can only be operated when DP'd to a standard locomotive with a crewed cab, which would be called the "A Unit". Very large cables are hooked up between the two (or more) units so that the trailing units operate off of the same control inputs that come back from the A unit. That B unit pictured is very likely older than the newer road engines on both ends of it, since it so closely resembles the older "Jeeps" that we commonly used for yard switching or short run turns.
Another version on that B unit is called a Slug, but unlike a B unit a Slug is shorter in height has no engine or generator so it doesn't produce its own power. It's basically used as an accessory to a standard locomotive, which transmits its electrical power back to the slug to power the slug's traction motors.
Those big road engines were fun to operate, I remember one trip where we were trying to take an empty coal unit train to western MN. Two locomotives on each end (4 total) with only one cut in for power on each end. We started having trouble not far into the trip though, every time we cut power on the lead unit the tail unit kept pushing - that was an experience lol.