"The Last Full Measure"; the charge of the First Minnesota Volunteers.
I've been to Gettysburg twice and have taken the march path of those volunteers from near the center of the battlefield to Plum Run. The route of Pickett's Charge from the Virginia Memorial to the stone wall is mowed and trimmed: the path of the First Minnesota is not.
That is as it should be. Once you get done snagging your clothing on brambles and thistles in the summer heat and scrambling over and through split-rail fences, you can't help but imagine doing it in wool clothing, knowing what the real volunteers faced at the march's end.
The First Minnesota, which was the first regiment offered to Lincoln after Fort Sumter, suffered the highest percentage of casualties in a single engagement that day than any formation in the United States Army during the Civil War.
Or, as the text of the Minnesota memorial at Gettysburg states:
"The loss of the eight companies in the charge was 215 killed & wounded. More than 83% percent. 47 men were still in line & no man missing. In self sacrificing desperate valor this charge has no parallel in any war."
The next day, the remnants of the First Minnesota Volunteers helped repulse Pickett's Charge, losing another seventeen men.