Concerning Chosin Reservoir in Korea, the battle there was really, really bloody and the Marines got cut up bad, but they were still there and needed some help withdrawing from the scene ~ plenty of material on the net can give you an idea of what went on there.
Some really bright guy somewhere in Department of Defense decided that the unit to send to "hold the door open" and serve as a "rear guard" for that withdrawal was the 1/15 Infantry ~ Audy Murphy's unit ~ in terms of military awards and battle streamers quite arguably the BEST Army Infantry there's ever been.
Whether they were really up to the task at the Frozen Chosen was beside the point ~ the Marines deserved the best and they got the best and the 1/15 accepted the honor.
BTW, our top supply sergeant at Harvey Barracks had been in the 1/15 Infantry "way back when" that happened.
whoops!! I meant to say O.P. Smith. Not Julian Smith, a WWII Marine General.