‘Unlike British regulars, these Americans discarded scarlet jackets for brown buckskins and rough linen hunting shirts dyed green to blend with the forest. [British Lieutenant Colonel] Abbott could hardly conceal his disdain, asking an American officer, Captain Edward Billings, why his troops weren’t properly in line and firing by volley. “The whole point of our training,” the American explained, “is to keep from exposing ourselves and learning to reload quickly and hit what we fire at.”
The British officer snapped, “You mean you specifically aim at the enemy?”
“If we don’t have a good target,” the American replied, “we don’t shoot.”
“In other words, if you saw an enemy officer, there may be 20 or more of you aiming at him?” When the American nodded, the British officer cried, “Why, that’s absolute murder!”
“No sir, Colonel, that’s not murder,” the American observed. “That’s war.” ‘
– Major John L. Plaster, 2008, The History of Sniping and Sharpshooting pp. 16-17 
I’m still reading through Plaster’s book The History of Sniping and Sharpshooting, and it’s a fascinating book. The above exchange took place shortly before the American Revolutionary War.
The book discusses the role of sharpshooters & snipers in various wars chronologically. I’m currently started the section on World War I, which means I’m a bit less than halfway through the book.
It’s a wonderful book, but also long. The text portion is over 600 pages, not including the bibliography.
Another part from the early section I found fascinating: Rogers Rangers’ Standing Orders.
Major Robert Rogers was one of the first military officers to ever put together a group made specifically of sharpshooters. These are the standing orders he created for them in 1755, during the French and Indian wars:
- Don’t forget nothing.
- Have your musket as clean as a whistle, hatchet scoured, six pounds powder and ball, and be ready to march at a minute’s warning.
- When you’re on the march, act the way you would if you were sneaking up on a deer. See the enemy first.
- Tell the truth about what you see and what you would do. There is an army depending on us for correct information. You can lie all you please when you tell other folks about the Rangers, but don’t never lie to a Ranger or an officer.
- Don’t never take a chance you don’t have to.
- When we’re on the march we march single file, far enough apart so one shot won’t go through two men.
- If we strike swamp or soft ground, we spread out abreast, so it’s hard to track us.
- When we march, we keep moving ’til dark, so as to give the enemy the least possible chance at us.
- When we camp, half the party stays awake while the other half sleeps.
- If we take prisoners, we keep ’em separate ’til we have had time to examine them, so they can’t cook up a story between ’em.
- Don’t ever march home the same way. Take a different route so you won’t be ambushed.
- No matter whether we travel in big parties or little ones, each party has to keep scouts 20 yards ahead, 20 yards on each flank and 20 yards in the rear, so the main body can’t be surprised and wiped out.
- Every night you’ll be told where to meet if surrounded by a superior force.
- Don’t sit down to eat without posting sentries.
- Don’t sleep beyond dawn. Dawn is when the French and Indians attack.
- Don’t cross a river by a regular ford.
- If somebody’s trailing you, make a circle, come back on your own tracks, and ambush the folks that aim to ambush you.
- Don’t stand up when the enemy’s coming against you. Kneel down, lie down, hide behind a tree.
- Let the enemy come ’til he’s almost close enough to touch. Then let him have it and jump out and finish him with your hatchet.
 Plaster, Maj. John L., The History of Sniping and Sharpshooting, Paladin Press, copyright 2008, ISBN 978-1-58160-632-4