The McDonnell Douglas (now Boeing) F-15 Eagle is a twin-engine, all-weather tactical fighter designed to gain and maintain air superiority in aerial combat. Developed for the United States Air Force, it first flew in July 1972, and is one of the most recognized modern fighters. The F-15 is expected to remain in service with the Air Force until 2025. Despite originally being envisaged as a pure air superiority aircraft, the design proved flexible enough that an all-weather strike derivative, the F-15E Strike Eagle, was later developed, and entered service in 1989.