Hennings was circuit attorney from 1941 to 1944, taking leave of absence in September, 1941 to volunteer in active duty in the United States Naval Reserve. Serving in the Pacific and Caribbean as a lieutenant commander for three years, he was discharged from active duty due to physical disability incurred in the line of duty. After which, he resumed the practice of law in the St. Louis firm of Green, Hennings, Henry and Evans.
