The 16th Connecticut was formed in Hartford County, Connecticut, in July and August 1862. It was mustered into service August 24, 1862 and became part of Mr. Lincoln's Army of the Potomac. Three weeks later the regiment first saw action at the Battle of Antietam, Maryland as part of Burnside's Ninth Army Corps. Having loaded muskets for the first time only the day before the battle, the regiment suffered significant casualties at Antietam. It next saw action at Fredericksburg, Virginia in December 1862, then at the Siege of Suffolk, Virginia in April/May 1863. In 1864, the 16th Connecticut, then with the 18th Army Corps, was part of the Union garrison at Plymouth, North Carolina, and vigorously defended Plymouth against a Confederate combined land and naval attack April 17-20, 1864 led by General Robert F. Hoke, C.S.A. Outnumbered more than 5 to 1, with no means of escape or opportunity for reinforcements, the Union garrison at Plymouth was surrendered on April 20, 1864 by Brigadier General Henry W. Wessells.