SPITFIRE: A Fighter Pilot's Story of World War II is made up of Captain Warren's diary entries reflecting his combat experiences during 1942-43, photos, and transcripts from a series of radio broadcasts which he participated in during his stint as a flight instructor at Craig Field (Selma, Alabama) during 1944.

In December 1940, Warren had passed the required exam for pilot training and was admitted into the United States Army Air Corps (USAAC) as an Aviation Cadet. He graduated from flight school in September 1941 (Class 41G) and was assigned to the 52nd Pursuit Group (after May 1942, it was renamed the 52nd Fighter Group).

Warren initially flew P-39 Airacobra fighters until his unit was shipped to the UK, where the 52nd was re-equipped with Spitfire Mk Vs, one of the best fighters of World War II. Warren was given extensive training in flying Spitfires from the Royal Air Force (RAF) and flew briefly on operations over Europe until the 52nd Fighter Group was shipped over to Gibraltar, wherefrom it flew into Algeria as part of the Anglo-American invasion of French North Africa in November 1942.

Warren's diary entries convey the fatigue, perils, fears, and hazards of wartime flying, as well as the lack of amenities on base that were typical during that phase of the North African campaign.

By the time, Warren was sent stateside in April 1943, he had taken part in 71 combat sorties and been credited with shooting down 2 Luftwaffe fighters in aerial combat.