A telephone switchboard operator and a portion of the "Red Air Force" was photographed at Fort Knox during Anti-Aircraft Artillery and Air Corps Exercises in May 1933.

Testing an air defense warning system proposed by Capt. Claire Lee Chennault, the AA-AC Exercises pitted new modern bombers against older and much slower biplanes. Friendly forces were based out of Dayton, Ohio, while the opposition forces, which included antiaircraft defenses, were based at Fort Knox. Observation posts were established between those locations.

When bombers were spotted, telephone operators at Fort Knox were notified of their location and airplanes were sent to intercept them. It was found that bombers could regularly be intercepted by these older airplanes and leaders concluded the cumbersome bombers would require friendly escorts for successful missions.

In the years following, the Air Corps would implement additional exercises for their bombers, which would be put to the test during the Second World War.