CONAN: Well, OK. Then he failed to use a third of his army in the battle.
THORP: That's what a lot of people say. I'm not exactly clear as to what that means by using a third of the army.
CONAN: There were two corps he never ordered into the fight.
THORP: What corps were those? The 6th Corps had troops that were on the frontline. Irwin's brigade had - I believe it was Irwin's brigade was engaged over by the Dunker Church. There were also some 6th Corps units that were involved in the Sunken Road. And also the 5th Corps, the entire 5th Corps was not even there. One of the divisions was still on the march. They marched 60 miles in three days. They wouldn't get there until the 18th. Another division, Morell's division, had just arrived, which is the only reserve that McClellan had. And then Sykes' division, the Third Division, was actually across the river and advancing up towards the center, alongside of Burnside's troops.