https://en.wikipedia.org/wiki/Little_Round_Top#Battle_of_Little_Round_Top

Chamberlain (knowing that his men were out of ammunition, his numbers were being depleted, and his men would not be able to repulse another Confederate charge) ordered his men to fix bayonets and counterattack. He ordered his left flank, which had been pulled back, to advance in a ‘right-wheel forward’ maneuver. As soon as they were in line with the rest of the regiment, the remainder of the regiment would charge akin to a door swinging shut. This simultaneous frontal assault and flanking maneuver halted and captured a good portion of the 15th Alabama.[17] While Chamberlain ordered the advance, Lieutenant Holman Melcher spontaneously and separate to Chamberlain’s command initiated a charge from the center of the line that further aided the regiment’s efforts.[18][19]

During their retreat, the Confederates were subjected to a volley of rifle fire from Company B of the 20th Maine, commanded by Captain Walter G. Morrill, and a few of the 2nd U.S. Sharpshooters, who had been placed by Chamberlain behind a stone wall 150 yards to the east, hoping to guard against an envelopment. This group, who had been hidden from sight, caused considerable confusion in the Confederate ranks.[17]

Thirty years later, Chamberlain received a Medal of Honor for his conduct in the defense of Little Round Top. The citation read that it was awarded for “daring heroism and great tenacity in holding his position on the Little Round Top against repeated assaults, and ordering the advance position on the Great Round Top.”[20]