CISX 500, a depressed centre flat car.

[Mr Fixit]

I am thinking that with a build date of October 1941, the car was built to handle larger ingots that would be needed to handle the vast amounts of armour plate required during a World War. At the time of building the car, the US was well along the road to becoming a war economy as it was already "The Arsenal Of Democracy" helping to to supply those already fighting the Axis forces with weapons and munitions, tanks, aircraft, trucks, and everything else required in time of war. Indeed at this time the US was in the twilight of is last days of "peace", gearing up and manning up for a war that was spreading around the world, and that would spectacularly burst forth on Sunday, December 7, 1941.

As I understand it, a larger ingot would retain it's heat longer following its pouring and then during transit between one plant and the next and, so reduce the amount of "soaking" time and energy required to bring it back up to heat prior to rolling at the next plant.

Mark