While a Confederate offensive into the North had failed in 1862 and resulted in substantial losses for both armies in the Battle of Antietam, recent victories over Union forces at Chancellorsville and Fredericksburg led Confederate military leaders to believe that the summer of 1863 was the time to press their advantage. Despite being outnumbered in recent battles, General Robert E. Lee was able to outmaneuver his forces by repeatedly dividing his army and attacking smaller detachments of the Union army rather than facing the entire Union force at once. Pushing northward into Pennsylvania, Lee hoped that he could avoid a pitched battle against the larger Union army by again maneuvering his soldiers quickly and attacking Union armies one at a time. If successful, he believed that a Confederate offensive could force the Union to send troops to meet his armies else he surround Washington. As a result, Lee hoped that he would be able to hold the high ground and attack in places and times of his choosing if he was on the offensive near the nation's capital.
Once again facing a larger Union army in the area but hopeful that he could attack and defeat Union forces before they could converge on his army, men under Robert E. Lee advanced into Gettysburg on July 1st. Hoping to prevent further Confederate movement, Union General Joseph Hooker established defensive lines on the outskirts of Gettysburg facing northeast. Lee’s army under A.P. Hill and reinforcements of Richard Ewell began an assault at Cashtown to the west of Gettysburg. This maneuver was a success, and the Confederate army pushed further towards Gettysburg, unaware of the size and exact location of union forces at Gettysburg.
After getting pushed from Gettysburg, the smaller Union forces in the area converged on Cemetery Hill just south of the town. The 20th Maine Regiment was the extreme left flank of the Army of the Potomac and located just southeast of Cemetery Hill. Thus, it was up to the forces positioned on the hill to prevent a flanking maneuver that would make the Union's position vulnerable. If the Confederates would have been able to force the 20th Maine to fall back, they could have attacked an exposed Union line that stretched several miles.
Recognizing the need to hold the Confederates back as long as possible, the 20th Maine endured a high casualty rate as they held their ground and repulsed attack after attack by the 15th and 47th regiments from Alabama. The Confederates responded by trying to get further and further to the right in hopes of out-maneuvering the 20th Maine. To counter this strategy, Colonel Chamberlain ordered his lines to step to the left and lengthen their lines to respond to the increasing threat of the Confederates attacking the flank. This maneuver stretched the Union lines and reduced the number of men along an increasingly thin line of defense. As a result, the actions of each soldier was vital to the survival of the entire regiment.
As the battle wore on, ammunition for both armies started to run low. The 20th Maine was not able to obtain supplies given their isolated and vulnerable position unless they retreated. As Chamberlain's forces spent their last rounds of ammunition, he ordered his men to fix bayonets and charge the Confederate line, an attack that shocked the tired Confederate soldiers who saw the bayonets and heard the screams of the swiftly advancing 20th Maine. Rather than fall back and give up their position and weaken the Union line, the 20th Maine took many of the Confederate attackers as prisoners.
The heroism displayed on this portion of the battlefield prevented a Confederate flanking maneuver and provided time for Union commanders to secure reinforcements. Furthermore, the lack of advance on the southern lines preserved the Union army’s interior lines and hold some of the higher ground. After fierce fighting on the first two days, the Union army forced Lee's army to retreat. General Meade made the fateful decision to allow the Southern army to leave Pennsylvania rather than pursing them.
Nearly 30 years later, Colonel Chamberlain was awarded the Congressional Medal of Honor for his actions at Gettysburg on July 2, 1863. The medal is now displayed at his alma mater Bowdoin College in Maine.