Woodie,
Go to the "sanity check" thread of Scratchin and Bashin. The photo of Southern Pacific #1001 is what is called a "slug". What the railroad has done is to remove the prime mover (diesel engine) and all associated equipment, rebuilt the hood to a lower height and filled the resulting carbody full of cement. This unit is then hooked up to another diesel locomotive by MU (multiple unit) cables. This locomotive, sometimes called a "mother", supplies power to the slugs traction motors. This results in the ability for this combination to run at extremely slow speeds (2 to 5 MPH). You will find these slug-mother combos mostly at major freight yards, such as SP's Colton Yard and Santa Fe's Barstow Yard.
Hope I wasn't to confusing.
Dan