Explanation: When the Americans learned of the Soviet Mig-25 'Foxbat', the US was certain that the high-speed jet shown by the Soviets was, due to its design and the classified nature of its technical details, an ultra-maneuverable ultra-fast fighter jet, and in response, poured money into the F-15 'Eagle' to make it a weapon that could compare to its Soviet counterpart!

Some ten years later a defector landed with a Mig-25 and handed it over to Western intelligence. Turns out, it wasn't maneuverable at all, or a fighter, for that matter. It was an interceptor made for catching nuclear bombers, and had all the maneuverability of stiff cardboard. Very fast, though! C'est la vie!