Booster?

I was able to get a cab tour of a CP engine a few months ago and they had an odd air gauge located under the brake handles in the cab that said "Booster". There was also an odd "tank" of some kind in the nose that my guide said had something to with it.

Anyone know what this is? They seem to be something exclusive to canadian units?

You'll find the answer where you posted this question under the CP Railway thread.