Tibbets enlisted in the United States Army in 1937 and qualified as a pilot in 1938. After the Japanese attack on Pearl Harbor, he flew anti-submarine patrols over the Atlantic. In February 1942, he became the commanding officer of the 340th Bombardment Squadron of the 97th Bombardment Group, which was equipped with the Boeing B-17. In July 1942, the 97th became the first heavy bombardment group to be deployed as part of the Eighth Air Force, and Tibbets became deputy group commander. He flew the lead plane in the first American daylight heavy bomber mission against Occupied Europe on 17 August 1942, and the first American raid of more than 100 bombers in Europe on 9 October 1942. Tibbets was chosen to fly Major General Mark W. Clark and Lieutenant General Dwight D. Eisenhower to Gibraltar. After flying 43 combat missions, he became the assistant for bomber operations on the staff of the Twelfth Air Force.