By 1997, the McDonnell Douglas F-15 Eagle was the U.S. Air Force's premier fighter, and more than 1,200 were in operational service. During operation Desert Storm, F-15 Eagles accounted for 36 of 41 enemy aircraft shot down in air-to-air combat. By 1998, the improved F-15E Strike Eagle was the world's most technologically advanced fighter, able to fly higher than 50,000 feet at more than Mach 2.5.