 He's watching this from the standpoint of his students. There were no electives in those days, so he would have taught every student who enlisted in the Union Army. They actually come at one point and begin drilling on the campus, and one of the leaders of the drill observes that Chamberlain comes with great curiosity. But it's not until 1862 when Lincoln says we now need 300,000 more men that then Chamberlain sends his enlistment to the governor of Maine.