Following his graduation from the U.S. Air Force Institute of Technology in 1954, Rushworth stayed at Wright-Patterson Air Force Base in Dayton, Ohio. Among his duties was to serve at the Directorate of Flight and All-Weather Testing. There he specialized in the development and flight testing of experimental automatic flight control systems. He graduated from the Air Force Experimental Flight Test Pilot School (Class 56C) in 1957, flying F-101 Voodoos, F-102 Delta Daggers, F-104 Starfighters, F-105 Thunderchiefs, F-106 Delta Darts and other jet fighters. Rushworth was selected for the X-15 program in 1958. He made his first flight on November 4, 1960. Over the next six years, he made 34 flights in the X-15, the most of any pilot. This included a flight to an altitude of 285,000 feet, made on June 27, 1963. This flight above 50 miles qualified Rushworth for Astronaut Wings, though he would have attained that honor sooner had the USAF Man In Space Soonest project proceeded according to plan.