The largest regimental loss of the Civil War was sustained by the 1st Maine Heavy Artillery at Petersburg.

The 1st Maine Heavy Artillery was a regiment in the Union Army during the American Civil War. It suffered more casualties in an ill-fated charge during the Siege of Petersburg than any Union lost in a single day of combat throughout the war. It was also the Union regiment with the highest number of officers killed. On June 18, 1864, 850 men of the 1st Maine Heavy Artillery were advancing through a cornfield as the Confederate line burst into flames. Support units failed to defend their flanks, and 1st Maine's men found themselves under fire that appeared to be hit from all angles. Within ten minutes, a staggering 632 men were dead or wounded in the fields, and not a single man had come close to the enemy lines.

All in all, the 1st Maine Heavy Artillery sustained one of the highest casualty rates in the war, with 423 killed, and another 260 died of disease. A monument to the 1st Maine stands on the former battlefield at Petersburg. The regiment is boasted by a monument on the Petersburg, where it suffered the greatest single day's loss in killed and mortally wounded of any in the Civil War. In just under a month of fighting, beginning with the battle at Harris Farm on May 19 and ending outside Petersburg on June 18, the 1st Maine Heavy Artillery lost a staggering 1,205 men out of the 1,800 it had started with when it arrived in Belle Plain. As can be seen, the 1st Maine Heavy Artillery is an indispensable name when it comes to one of the facts about the Petersburg campaign.