The merger of McDonnell and Douglas allowed each company to profit from its successful specialties. McDonnell, in fighters, began work in 1967 on the successor to the F-4 Phantom, the F-15 Eagle. The F-15 made its first flight in 1972 and entered service in 1974. It went on to shatter all existing records and fly with air forces in Israel, Japan, Saudi Arabia and South Korea. What distinguishes the Eagle from all other aircraft of its time is the power of its two engines; their thrust is greater than the weight of the fully loaded plane. It can climb straight up, accelerating to supersonic speeds. The latest version of the F-15 is the F-15E Strike Eagle dual-role fighter. It can perform air-to-ground as well as air-to-air missions in all weather conditions. By June 2004, the F-15 had a perfect combat record of 101 aerial victories and zero defeats.