Robert Dunlap was born in Abingdon, Illinois. Before graduating from Monmouth College, Dunlap enlisted in the US Marine Corps Reserve in March 1942. After graduating, Dunlap attended Officer Candidates Class at Quantico and was commissioned as a Second Lieutenant. He then attended Parachute Training School, joining the 3rd Parachute Battalion.
In 1943, he participated in the invasions and subsequent fighting on Vella Lavella, Bougainville, and the Solomon Islands. With the dissolution of the parachute battalions, Dunlap was assigned to the 5th Marine Division and became the commanding officer of C Company, 1st Battalion, 26th Marines. Over the first several days of the Iwo Jima campaign in February 1945, Dunlap repeatedly put himself in harm’s way in order to call in artillery fire to bombard Japanese positions. On February 26, Dunlap was shot in the left hip, but survived, spending 14 months recovering from his wounds.