The F-15 has a Control Augmentation System (CAS), and would be difficult to fly without one: http://www.f15sim.com/operation/f15_flight_control_system.ht.... Fly-by-wire means there is no hydraulic/mechanical control system, and is a relatively new feature. But computers have been "in the loop" with conventional hydraulic/mechanical control systems for quite a bit longer, especially in fighter planes, where the emphasis on maneuverability calls for airframes that are a lot less statically stable and would be hard to fly without control augmentation.