Is an unsung hero. If not for John Buford, commander of the advance of the Union Cavalry... Chamberlain's heroics, and Pickett's charge may never have happened.
He arrived just ahead of Confederate forces advancing on Gettysburg. He quickly recognized the strategic importance of the ground around him. He had the high ground, and he was determined to hold it at all costs. General Buford arranged his men brilliantly. The opening shots fired by his men took the advancing Confederates by surprise.
Buford only had two Brigades. Two Brigades to stand against the advance elements, of the Army of Northern Virginia. If prior to the battle you had told it's commander this... General Robert E. Lee would have smiled. Up till this point, Union Cavalry had earned a poor reputation. However, Union troopers were about to make their mark on history.
Surprised by the Union fire, but disciplined...the Confederates began to deploy in line of battle. This took time however, time which Buford needed. He knew that John Reynolds in command of the 1st Corp was fast approaching. If he could just hold till then. This is where his tactics came into play. His defense in depth was textbook, and his men executed it superbly. By making use of the terrain, he delayed the enemy's advance. He held long enough for the troops under General Reynolds to arrive and deploy.
However, even with the arrival of the 1st Corp, Union forces were still outnumbered. Fighting was heavy, and sadly, General Reynolds had been killed. He was admired by his men and peers. He was considered to be the best General in the Union Army. He had approved of Buford's plan. With the deployment of his Corp, he had committed the Army of the Potomac to the coming fight. Despite a spirited defense, Union forces were forced to retreat south.
However, thanks to the leadership of John Buford, the skill and bravery of his men... the Army of the Potomac, had gained the strategic high ground south of Gettysburg. Despite repeated and furious attacks by Confederate forces, the north never relinquished this ground. The Army of Northern Virginia was forced to retreat. It would never again be an offensive threat.
Little Round Top, The Devil's Den, and Pickett's Charge take precedent in history, and with good reason. However, the opening of the battle, which has no name, also deserves it's place. If John Buford and his troopers, had not been able to hold the high ground... if they had not been able to buy time... the events of those early days in July of 1863, might have turned out far differently.