There were 3 regiments that incurred extraodinary % losses in the McPerson/Herbst Woods areas.
But the answer is 24th Michigan and the 26th North Carolina as they directly met.
On the Union side.
The 2nd Wisconsin had a 79.5 % casualty rate. [302] 29k, 16mw, 135w, 18w-c, 42m = 240 79.5%
The 24th Michigan had 74.8% casualty rate. [496] 71k, 25mw, 186w, 13w-c, 76m = 371 74.8%
On the Confederate side.
The 26th North Carolina had an 81% casualty rate. [
839] 172k, 332w, 72m = 687 81.0%
I recognize the pitfalls of casualty reporting during the CW. Plus the 26th NC had the misfortune of participating in the PPT day 3 charge which elevated their casualties. Plus the Iron Brigade incurred casualties from Archers brigade prior to the arrival of the 26th NC.
The 24th Mi had the 19th Indiana and the 2nd Wisconsin to their immediate north. Their successful delaying action set the stage for the battle.
I frequently take the path behind the 26th NC monument down to Willoughby Run to walk in their foot steps. I just posted this in the Gettysburg board. I believe that this fight is one of the most important acts in the battle.
I would love to see a higher combined casualty rate than these regiments saw in any CW battle. Their actions are remarkable.
For those interested, a nice read resides here.
http://www.civilwar.org/battlefields/gettysburg/gettysburg-2011/the-battle-for-herbst-woods.html