Vance H. Marchbanks, an African-American soldier and scientist, was "born in the service" in Wyoming where his father, a cavalry captain, was stationed. After receiving a bachelor's degree from the University of Arizona and an M.D. from Howard University, Marchbanks completed his internship and residency in Internal Medicine at Freedman's Hospital in Washington, D.C. After that he served as a medical staff member at the VA hospital in Tuskegee, Alabama, until he entered the Air Force in 1941. Marchbanks served as group surgeon in Italy and was eventually awarded the Bronze Star.

During the Korean War, Marchbanks gained further experience in aviation and medicine, accruing over 1,900 hours in prop and jet aircraft flight, gathering valuable medical data that later appeared in research publications and military manuals. In 1957 he participated in a 10,600-mile (17,066-km) nonstop flight from Florida to Argentina to New York in a B-52 jet bomber. Studying crew comfort and fatigue during the flight, Marchbanks found that the adrenal hormone content in blood and tissue was an indicator to the physical fatigue which often preceded a fatal crash. This discovery earned him an Air Force Commendation Medal. Marchbanks also received a medal for developing an oxygen mask tester, later adopted by the Air Force, which encouraged air crew members to clean their masks frequently.

With his extensive military service and his rating as a chief flight surgeon (rare because it required 1,500 flying hours and 15 years on flying status), Marchbanks was assigned to the Project Mercury space program in 1960. He prepared for this new role by sitting in on aerospace lectures, studying each astronaut's medical history, and visiting tracking stations used for the space flights. From a tracking station in Kano, Nigeria, Marchbanks monitored John Glenn (1921-) on his famous Mercury flight in February 1962. Marchbanks monitored Glenn's respiration, pulse, temperature, and heart reactions through electronic sensing devices attached to the astronaut and set up to relay the information to ground recorders. With his months of preparation, Marchbanks was able to compare Glenn's practice mission electrocardiograms with the actual ones recorded during the mission. He was relieved to note normal tracings throughout the flight. Marchbanks eventually headed up a medical hospital at an Air Force base in California.