The German Railroad purchased well over 3,000 sliding roof / sliding wall boxcars in the Fifties and Sixties as general-purpose units for hauling weather-sensitive freight. Their great advantage lay in the steel sliding walls and sliding roof cover that could be opened easily. These cars could be loaded very quickly with a forklift truck.
Prototype: German Federal Railroad (DB) type Kmmgks 58 sliding roof / sliding wall car without a hand brake. The car looks as it did in Era IIIb. Car number 370 047.