Over 700 different aircraft models were used during World War II. At least 135 of these models were developed for naval use, including about 50 fighters and 38 bombers. Only about 25 carrier-launched aircraft models were used extensively for combat operations. Of these, nine were introduced during the war years after the attack on Pearl Harbor, four by the United States Navy (USN) and three by the Royal Navy (RN) and two by the Imperial Japanese Navy (IJN).