"[instructing Chamberlain on troop movements] Line of battle consists of two lines of men, one behind the other, so that while one line fires, the other reloads. Behind them is a line of file closers - lieutenants and sergeants. But two lines make a regiment unwieldy on the move, so we need to switch to column of fours. We need to be able to change from column of fours into line of battle and back again quickly. It is not difficult to move from line of battle to column of fours. It is much harder to move from column of fours into line of battle, and if we're called upon to make that move, it will be when we're under fire. I'm sure you can understand, Colonel, how important it is that these moves are learned so thoroughly that the men could perform them in their sleep."