That was one specific station - the infamous WLW / W8XO - the first and only US station authorized to operate at 500kW of power.[1]
To give you an idea of how powerful that is, take a look at their coverage map: http://i.imgur.com/Aigz1Zh.jpg
The back story is kind of interesting. It was run by Powel Crosley - a sort of 1930's version of Elon Musk. Advertising revenues from the station were so successful he applied to increase the limit from 500kW to 750kW(!).
It's a big deal in the ham community, but I only learnt latter that while US stations were limited to 50kW - other parts of the world didn't have such restrictions. Parts of the Middle East have 2,000kW stations. [2]
You can get a full download on the Crosley WLW station in this video: https://www.youtube.com/watch?v=CbHjcwIoTiY