As we know some nations (e.g. Soviet Union) bestowed "Guards" title on their elite units, thus distinguishing them from "line" units. Would it be possible to have same distinction in US military? Having access to best equipment and people but also given hardest missions. They don't have to be called Guards, it can be something else that denotes their elevated status and it has to be small part of overall combat units
Maybe during ACW such title is given to units that distinguished themselves in battle and then it's carried on later?