Little Round Top was undefended by Union troops. Maj. Sickles, defying Meade's orders, moved his corps a few hundred yards west to the Emmitsburg Road and the Peach Orchard. When Meade discovered this situation, he dispatched his chief engineer, Brig. Gen. Gouverneur K. Warren, to attempt to deal with the situation south of Sickles' position. Climbing Little Round Top, Warren found only a small Signal Corps station there. He saw the glint of bayonets in the sun to the southwest and realized that a Confederate assault into the Union flank was imminent. He hurriedly sent staff officers, including Washington Roebling, to find help from any available units in the vicinity.^[79]

The response to this request for help came from Maj. Gen. George Sykes, commander of the Union V Corps. Sykes quickly dispatched a messenger to order his 1st Division, commanded by Brig. Gen. James Barnes, to Little Round Top. Before the messenger could reach Barnes, he encountered Col. Strong Vincent, commander of the 3rd Brigade, who seized the initiative and directed his four regiments to Little Round Top without waiting for permission from Barnes. He and Oliver W. Norton, the brigade bugler, galloped ahead to reconnoiter and guide his four regiments into position.^[80]

Upon arrival on Little Round Top, Vincent and Norton received fire from Confederate batteries almost immediately. On the western slope, he placed the 16th Michigan, and then proceeding counterclockwise were the 44th New York, the 83rd Pennsylvania, and finally, at the end of the line on the southern slope, the 20th Maine. Arriving only ten minutes before the Confederates, Vincent ordered his brigade to take cover and wait, and he ordered Col. Joshua Lawrence Chamberlain, commander of the 20th Maine, to hold his position, the extreme left of the Army of the Potomac, at all costs. Chamberlain and his 385 men waited for what was to come.^[81]