Perhaps in other war was the esprit of the regiment more vital or apparent than in the civil war. The regiment became a second home; usually the men were from the same area, and they often had known each civilian life while there was pride in nation, army corps, division, and brigade it was the regiment that usually counted most.
For the Union, 3559 separate units included regiments; separate battalions, companies, or batteries of this total 2144 were infantry regiments, 272 cavalry regiments, 61 of heavy artillery, 13 of engineers, 9 light infantry battalions, and 432 separate batteries
Among the northern infantry regiments the fifth new Hampshire suffered the most in total killed or dead of wounds 295 including 18 officers the eighty third Pennsylvania was second with 282 including 2 officers followed by the seventh Wisconsin with 281 fifth Michigan twentieth Massachusetts 260; sixty-ninth new York 259; and of wounds to those enrolled how ever the list is different with 23 regiments having 15 percent or more losses. The second Wisconsin with 1203 men enrolled lost 238 killed 19.7 per cent, followed by the first marine heavy artillery with 423 killed out of 2202 enrolled, for 19.2 per cent. The fifty seventh Massachusetts had 201 killed or mortally wounded out of 1052 for 19.1 per cent.
While figures are often disrupted, the largest of killed or mortally wounded suffered by one unit in anyone engagement for the north seems to have been he first marine heavy artillery with 210 fatalities at Petersburg, June 18, 1864. In fact, heavy artillery appears to have suffered considerably. Second is the eighth New York heavy artillery with 207 fatalities at Cold Harbor in June 18 1864. In infantry regiments the fifth New York had 117 fatalities at second Bull Run or Manassas; followed by the fifteenth New Jersey with 116 at Spotsylvania; forty ninth 109 at Spotsylvania; fifteenth Massachusetts, 108 at antietam; first Kansas at Wilson’s creek, mo., 106; first Missouri at Wilson’s creek, 103; ninth Illinois at Shiloh or Pittsburgh landing, 103; eighteenth u.s. infantry, stone’s river or Murfreesboro, 102; eleventh Illinois fort donelson, 102.
As to percentage of a regiment killed or mortally wounded in any one engagement, the leader was the first Minnesota, which had 262 engaged, lost 50 dead and 174 wounded (25 of whom died later) for 224 causalities at Gettysburg July 2. Thus, fatalities number 75, or over 28 per cent. Next was the fifteenth New Jersey at Spotsylvania, which lost 116 killed or mortally wound out of 432, a loss 0 of 26 per cent in the several days of that battle. At Cold Harbor the twenty-fifth Massachusetts had 310 reported for duty. Of that number 74 were killed or mortally wounded for 24 percent plus 118 more wounded and 28 missing. Several other regiments suffered 20 per cent fatalities or more in single battles.