Still with early diesel locomotives, today is an EMD SW7 switching type locomotive. Basically they were use to assemble trains in a switch yard. Some were used for industrial purposes. EMD built the SW7 between 1949 and 1951. It had a supercharged V12 diesel engine.
My models are made by Athearn. It is a cow (the unit with a cab) and a calf (the slave unit with out a cab). They are painted in Southern livery. I can’t remember if I bought these new or used. I several EMD yard switchers. I bought one set used and one set new.