Serving as an automatic rifleman with Company G, 2nd Battalion, 9th Marines, 3rd Marine Division during the bitter fighting on Iwo Jima, Watson earned the Medal of Honor for heroism during February 26–27, 1945, when he single-handedly killed more than 90 Japanese and enabled his pinned-down platoon to continue the advance. In the attack, he was shot seven times and was hit in the shoulder by mortar fragments. He was evacuated from Iwo Jima after he suffered a gunshot wound in the neck on March 2, 1945. He previously saw action at Bougainville, Guadalcanal, and Guam.