Overhead ice bunker cars had been proposed as early as the  late 1800s. Experimental cars were built by several railroads, but none were built in quantity.

In 1936-7 that the Canadian National and Canadian Pacific built twelve experimental cars to various designs utilizing overhead ice bunkers. Rather than drawing inspiration from past design concepts in North American railroading, the Canadian engineers instead traveled to South Africa and Hungary to study the overhead bunker reefers used by their railroads.

As with prior experimental cars, it was found that more product could be loaded, kept at cooler temperatures, with less ice and requiring fewer stops for re-icing enroute. The CN was happy enough with their performance that 100 more cars were built in 1939-1940, and by the late '50s the Canadian National and Canadian Pacific rostered over 6,000 cars.

Although a deemed a success by the Canadian railroads, other North American railroads did not follow suit. Ironically, this appears to be in part due to their efficiency. Reefers were primarily owned and operated by private car lines and not the railroads. These lines were paid based on mileage, and not the weight of goods carried. Thus, more efficient reefers that could carry more goods reduced the number of cars needed and the corresponding revenue.

The major spotting feature of the Canadian overhead ice bunker reefers was their eight roof hatches, rather than the standard four. Due to the overhead bunkers, the doors are shorter than on other reefers of the era.

There are minor differences between the designs built by the two roads and, as with all designs built over a number of years, new technologies and features were incorporated.