Cowell Van Deventer was taking flight instruction at Lambert-St. Louis Field in 1941 at St. Louis, MO. In March 1941, he joined the Royal Canadian Air Force and received his wings at the No. 14 Service Flying Training School at Aylmer, Ontario, on 23 October 1941. He flew with the RCAF in the Battle of Britain. Van Deventer was discharged from the RCAF on 24 September 1942 and transferred to the U.S. Army Air Forces.



On 8 July 1944, Captain Cowell Van Deventer was serving as Pilot of P-47 Thunderbolt 42- 26654 in the 410th Fighter Squadron, 373rd Fighter Group, Ninth Air Force, U.S. Army Air Forces.



On that day, CPT Van Deventer's unit was in action against German forces. CPT Van Deventer was leading a combat patrol at 24,000 feet when he spotted four P-47 Thunderbolts in aerial combat against 8 German fighters at 5,000 feet. After radioing the P-47s that his flight was coming to their aid, he and his men began a dive to 5,000 feet. One of the 8 German ME-109s broke off from the fight and headed inland. CPT Van Deventer gave chase and shot the plane down from a distance of about 50 yards. Ten miles away, CPT Van Deventer spotted another ME-109 at low altitude and, by flying 100 feet above the ground, was able to get under the German fighter and give him a fatal burst from his guns. CPT Van Deventer's courageous actions and extraordinary heroism that day earned him the U.S. Army's second highest award for valor, the Distinguished Service Cross.



The double kill on 8 July was the second for CPT Van Deventer. In 1943 in Tunisia, Africa, he shot down a Focke-Wulf 190 as it took off from an airport and downed a second plane by clipping it with his wing. CPT Van Deventer was credited with destroying four enemy aircraft in aerial combat during World War II.