While serving in operations in Quang Tri Province in Vietnam on February 5, 1969, Noonan's company was directed to move from a position they had been holding southeast of the Vandergrift Combat Base in A Shau Valley to an alternate location.
As the Marines commenced a slow and difficult descent down the side of the hill, made extremely slippery by the heavy rains, the leading element came under heavy fire from a North Vietnamese Army unit occupying well-concealed positions in the rocky terrain.
Four men were wounded, and repeated attempts to recover them failed because of the intense hostile fire.
Noonan moved from his position of relative security and, maneuvering down the treacherous slope to a location near the injured men, took cover behind some rocks. Shouting words of encouragement to the wounded men to restore their confidence, he dashed across the hazardous terrain and commenced dragging the most seriously wounded man away from the fire-swept area.
Although wounded and knocked to the ground by an enemy round, Lance Corporal Noonan recovered rapidly and resumed dragging the man toward the marginal security of a rock. He was however, mortally wounded before he could reach his destination. His heroic actions inspired his fellow Marines, who initiated a spirited assault which forced the enemy soldiers to withdraw.