Roeliff Brinkerhoff for the US, and Evan Peregrine for the Brits
Edit - I can't verify that anyone named Evan Peregrine was associated with a book called "The Volunteer Quartermaster." Since the question specifically asked about a Union quartermaster and not a British quartermaster, I can't consider Peregrine a correct answer to this question.
Finding the name was easy enough, but I was glad we had not to answer to any other question concerning Evan Peregrine! I have found nothing about him!
Edit - I can't find anything about Evan Peregrine myself, but according to one of your fellow players, he was a British soldier and therefore does not fit the question, which asked specifically about a Union quartermaster.
Again, don't worry about the answer to this question, since it will not be counted in the scoring for March.