The (highly-unofficial) Marine Corps Rules for Gunfights are tacked to the wall at a Marine outpost in the Iraqi town of Anoh in the Euphrates River Valley. Among the rules:

Have a plan. Have a backup plan because the first plan won't work. The faster you finish the fight, the less shot you will get. Be polite, be professional, but have a plan to kill everyone you meet.

— Tony Perry in Anoh, Iraq