I believe it was the land grant railroads the had to handle government shipments at half price. IIRC the practice ended right after WWII.

In reading about WWI the government shipped all kinds of supplies to the east coast for shipment to Europe. They were very poor at logistics and had most of the car fleet sitting in yards on the east coast waiting for ships. At the same time there were car shortages across the rest of the county caused by government incompetence. Of course, they didn't blame themselves and took over the railroads to cover their incompetence.