As Parker F. Dunn boarded the train for Camp Dix, New Jersey, he remarked, "I want to do something big for my country." He felt the call to serve when the United States entered into World War I in April 1917. Rejected from enlistment three times due to his eyesight, he refused to give up and finally entered the Army in April 1918 as an infantryman.

Dunn deployed to France as part of a newly formed Intelligence Section in A Company, 1st Battalion, 312th Infantry Regiment, 78th Infantry Division. He was with the 78th Infantry when it attacked enemy forces near St. Mihiel, France, in September 1918. As part of the Intelligence Section, Dunn gathered information and observations from the front lines for his battalion commander.

The following month, in the Argonne Forest near the village of Grand-Pré, the 78th Infantry Division came under heavy German machine gun and artillery fire that forced American troops to jump into a nearby river for cover. Dunn and the Intelligence Section were tasked to build a bridge to gain better access. When the 78th's commander needed to get a message to one of his battalions, giving them the mission to exploit a weakness in the German defenses, Dunn courageously volunteered for the mission.

His Medal of Honor citation provided details: "After advancing but a short distance across a field swept by artillery and machinegun fire, he was wounded, but continued on and fell wounded a second time. Still undaunted, he persistently attempted to carry out his mission until he was killed by a machinegun bullet before reaching the advance line." Shortly after Dunn died, the 2d Battalion, 311th Infantry, ascended Talma Hill and penetrated the enemy position, allowing the Americans to take Grand-Pré. This facilitated the American advance on 1 November 1918, contributing to the final successful push by the 78th Infantry Division.

In 1922, Pfc. Parker F. Dunn's father accepted his son's Medal of Honor. In 2012, Pfc. Dunn was posthumously inducted into the MI Hall of Fame and the Chief of the MI Corps dedicated a barracks on Fort Huachuca in his honor.