Musket drill, circa 1791
According to this page, the American 1791 drill manual was almost a literal translation of the French manual of the same year. Count on governments to make a complicated process even more complicated. In place of taking aim, the manual instructs:
"Let the muzzle be below the level of the eye a little, and the right elbow kept lowered, without being pressed against the body; shut the left eye; look along the barrel with the right eye; sink forward the head towards the butt in order to level; and place the fore finger on the trigger.
83. Apply, with force, the first finger on the trigger, without lowering or turning the head more, and remain in that position.”
1) I've seen the ORIGINAL of a late 17th century manual on musket reloading, in Library of Congress Rare Books collections. It had not a word in it, after the title page, everything was huge (maybe 12 x 18") images of what the next position looked like. I wonder for a while and then realized -- at that time, how many musketeers would be literate anyway? You showed them the picture and gave a verbal explanation. This original was amusing because on the back side of the pages were brown ink doodles of guys in 17th century clothing.... doodles by a person or persons dead for centuries.
2) The evolution of commands begins, if I recall correctly, in the 17th century, when the Dutch rediscover the Roman system from reading Josephus.... don't divide your army into three gigantic units, or "battles," divide them into smaller units, for flexibility. Then, because tactics became more complicated than push ahead and see who wins, they started with "short sentence" commands, eventually evolving to the modern drill form, where the first word or words clue what the command will be, and the second gives the signal to execute it. RIGHT ... FACE. STAND AT ... EASE. COLUMN OF FILES FROM THE RIGHT ... COLUMN RIGHT.
By the Civil War, things were getting complicated. If I remember, the skirmish line (groups of four sent ahead and free to take cover, etc.) had 27 bugle commands to follow, to advance, move in different directions, and rejoin their regiment in different ways. The system was intended to let units deploy into 2 or 4 man deep lines for fighting, without or without skirmishers, and then quickly reform into columns of 4 or so men to move down narrow roads, then repeat the process quickly (since your opponent was not going to watch passively while troops tried to form a firing line).