Got a US railroad question someone will know.

I'm trying to recall the name (& model designation) of the Gas Turbine powered locomotives the Union Pacific RailRoad used in the 50s and 60's - they were mostly used in the lines over the Rockies as I recall.

Anyone know? (and any useful links to sites about it would be good to).
I read a interesting book about them a few years back and can't recall the info now.

Also, anyone know if anyone has built or is building a MTS simulation of one of these? (now driving one of those would be so cool over the Marias Pass).

BTW: This UP Locomotive is not the "Big Boy" - as those were a Steam powered locomotive.