"..although I did wonder why the US Army MP brigades weren't enough."

David,
It is my understanding, based on an article I wrote and conversations I've had, that the Army is uninterested in re-establishing Constabulary units (which is what these law enforcement BNs sound like) because the Army doesn't think it ought to perform such missions.

Our MP brigades are not designed to perform constabulary/ gendarmerie duties though I think they could transition rather quickly for such duty if needed. But given that the Army seems more interested in returning to a pre-9/11 mindset and training focus (big, conventional wars vs small wars/ stability ops), it's good that the Marines are taking this on as we will quite likely need such a force during the next few years (Syria?). Just my two cents.