Secret Service Operator #5; America's Undercover Ace. Chicago, Illinois: Popular Publications, Inc., April 1934

Secret Service Operator #5; America's Undercover Ace. Chicago, Illinois: Popular Publications, Inc., April 1934, Volume: Gilbert C456. Robert L. Gilbert First Issues collection, Gilbert. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/527407 Accessed March 24, 2026.