The 1st Maine Heavy Artillery Regiment 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 regiment lost in a single day of combat throughout the war. It was also the Union regiment with the highest number of officers killed (23). All in all, the 1st Maine sustained one of the highest casualty rates in the war, with 421 killed, and another 260 dead of disease. A monument to the 1st Maine stands on the former battlefield at Petersburg.