During World War I Post wanted to become a pilot in the U.S. Army Air Service (USAS). Joining the training camp at the University of Oklahoma, he learned radio technology. Germany surrendered before he completed his training, the war ended, and he went to work as a "roughneck" in the Oklahoma oilfields. The work was also unsteady, and he turned briefly to armed robbery. He was arrested in 1921 and sent to the Oklahoma State Reformatory, serving more than a year there, and was paroled in the summer of 1922. In October 1926, Post was badly injured in an oil-rig accident when a piece of metal pierced his left eye. An infection permanently blinded him in that eye, and he typically wore an eyepatch thereafter.