Air Force and Marines aircraft are at war with each other. But it's all just  practice for the real thing. In the 1970s, the U.S. Air Force and Navy began training their pilots to fight against other types of aircraft, rather than the then-standard practice of just having practice air combat against each other. Now air force pilots, in F-16s, and marine pilots, in F-18s, practice air combat against each other. In addition to differences in aircraft (the F-18 is larger than the F-16, and has two engines), the two services have many small differences in how they operate in combat. Theres also the service rivalry angle, and the natural competitiveness of fighter pilots. A recent training exercise held in South Korea had F-16s based in South Korea practicing against marine F-18s based in Japan. The late model F-16Cs and F-18Ds are evenly matched on paper, so it all came down to pilot skill and tactics. An educational time was had by all.