The 20th Maine was organized in the state of Maine and mustered into Federal service on August 29, 1862, with Col. Adelbert Ames as its commander. It was assigned to the Army of the Potomac in the 3rd Brigade, 1st Division, V Corps, where it would remain until mustered out on July 16, 1865. At that time, the brigade also consisted of the 16th Michigan, the 12th, 17th, and 44th New York, 83rd Pennsylvania Volunteer Infantry regiments, and a Michigan company of sharpshooters.
Combat history
Prior to their notable actions at Gettysburg in July 1863, the regiment was held in reserve at Antietamin September 1862, was among those forced to remain overnight within sight of the Confederate lines at Fredericksburg in December 1862, forcing the regiment's Lt. Col. Joshua Chamberlain to shield himself with a dead man. The unit was unable to participate in the Battle of Chancellorsville in April-May 1863, due to a quarantine prompted by a tainted smallpox vaccine that had been issued to the unit's soldiers. On May 20, 1863, Colonel Ames was promoted and was succeeded as colonel and commander of the regiment by Lt. Col. Joshua L. Chamberlain, who had been offered and declined leadership of the unit at the time it was formed.
Gettysburg and Little Round Top
The most notable battle was the regiment's decisive role on July 2, 1863, in the Battle of Gettysburg at Gettysburg, Pennsylvania, where it was stationed on Little Round Top hill at the extreme left of the Union line. When the regiment came under heavy attack from the Confederate 15th and 47th Alabama regiments, the 20th Maine ran low on ammunition after one and a half hours of continuous fighting; it responded to the sight of rebel infantry forming again for yet anotherpush up the slope at them by instead suddenly charging downhill with fixed bayonets, surprising and scattering the Confederates, thus ending the attack on the hill and the attempt to flank the hill position and move around the south end of the Federal "fishhook". The 20th Maine and the adjacent 83rd Pennsylvania together captured many men from both Alabama regiments, as well as several other men of the 4th Alabama and 4th and 5th Texas regiments of the same division. Had the 20th Maine retreated from the hill, the entire Union line would have been flanked, endangering and hurting other Union regiments in the vicinity.
The 20th Maine marched from Appomattox, Virginia, on May 2, reaching the national capital at Washington, D.C., on May 12, where the remaining original members were mustered out of service on June 4, 1865, with the remainder of the regiment leaving the Federal service on July 16. The heritage of the 20th Maine is carried on today by the 133rd Engineer Battalion, Maine Army National Guard.
