Cpl. John Renfro, a radar technician with Headquarters and Headquarters Squadron airfield electronic maintenance division races a student during a fitness challenge at Miller Elementary School, Nov. 7. The Single Marine Program holds a fitness challenge once a month to teach students educational physical fitness. - Cpl. John Renfro, a radar technician with Headquarters and Headquarters Squadron airfield electronic maintenance division races a student during a fitness challenge at Miller Elementary School, Nov. 7. The Single Marine Program holds a fitness challenge once a month to teach students educational physical fitness.