Tell me about this keg/cask

I had an employee give me this old keg he had for a while. I was supposed to see that it was some kind of cask, as I have been wanting to get into cask beers for a while. I think it has 3 openings, on of which is a wooden bung. Firestone is stamped above the wood bung, and on one end it says Anheiuser Busch. Did they ever put any beer in casks? What do I have here? Would I be able to use this for cask beer?

It's a Firkin:
https://www.google.com/search?q=firkin&hl=en&sa=N&prmd=imvns&tbm=isch&tbo=u&source=univ&ei=ntd-UP_jLMnDyQHi8IDwBg&ved=0CFgQsAQ&biw=1920&bih=911