Captain Mulhollen was the pilot in a F-82 Twin Mustang night fighter with the 68th Fighter Interceptor Squadron, 6160th Air Base Wing. On May 26, 1951, while on a weather reconnaissance mission 20 miles north of the 38th parallel, contact was lost. He was listed as Missing in Action and was presumed dead on January 31, 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.