Jemiba said:
To my opinion, the rejection of the Mirage III and the preference of the F-104 just was a result of the "nuclear sharing", that means of the German ambitions to provide launching systems for nuclear weapons....The only country able and willing to supply such weapons to Germany then were the US, so the choice of an aircraft somehow was predetermined....
There may be some truth in that, although we need to remember that the US was perfectly willing to supply nuclear weapons for British designed Canberras and Valiants.
I suspect that the Germans preferred the F-104 because it was the better aircraft, given Germany's perceived requirements. The Mirage (or almost any of the other contenders) would probably have made a better fighter. But Germany did not want a fighter. It wanted a bomber, with, as you note, nuclear capability. I suspect that Germany referred to the required aircraft as fighter due to the political and historical sensibilities of the time. Given the perceived tactical situation at the time, the Mirage would have made a poor bomber, while, quite serendipitously, the F-104, would have seemed near perfect.
From the end of WW2 through the late 1950s, bombers were designed to achieve the maximum possible height over the target. Altitude gave the attacker a critical time advantage. Given a high enough approach, a bomber could bomb its target and depart before an interceptor could respond to an alert and climb up to attack altitude. Good altitude performance demanded comparatively large wing area and low wing loading. The chosen wing planform depended on the lift-to-drag ratio required for a given speed. Subsonic aircraft like the B-47, B-52, Valiant, and Victor were given large-area high aspect ratio, moderately swept wings. Later supersonic equivalents like the B-58 received an equivalent, large-area planform with the low aspect ratio required for low drag at supersonic speed: the delta wing.
The Mirage was designed as a light, fast-climbing, supersonic interceptor capable of reaching a high-altitude bomber in time to make an attack. Like the larger and heavier F-102, F-106, and CF-105, it adopted the same delta wing for the same reason the B-58 did: large area for good climb and maneuverability at altitude combined with low supersonic drag.
But at the time when the F-104 was selected, the West's bomber forces were changing tactics. Radar warning and tracking, guided surface-to-air missiles, and supersonic, ground-controlled interceptors like the Mirage appeared to eliminate the high-altitude bomber's advantages. To survive and carry out their missions, bombers had to regain their time advantage over the defense. It looked like they could do so by flying fast and low. Air-defense radars that gave reliable, long-range, early warning of high-level attacks generally performed badly against low-level targets. Detection ranges were short, so the radar nets could give little or no advance warning.
When B-52s and Valiants were assigned to high-speed, low altitude missions, however, airframes and aircrews suffered severely. Low-altitude air is turbulent, and airplanes with large wing areas and low wing loading respond immediately and violently to every gust and bump. Flying such an airplane at low level was be like driving a light, responsive sports car too fast on a washboard road: gusts and rough air that would be inconsequential at lower speeds subject pilot and airframe to such high frequency pounding that loss of control or structural failure are real dangers. When I was a boy, I visited the Johnsville Naval Air Development Center, where the US Navy did physiological and structural testing. They showed us a rig that simulated what pilots might face in low-level transonic flight. As I remember it, the instrumented test dummy and his ejection seat were just a blur. Experience and laboratory work like that at Johnsville quickly showed that aircrews could operate retasked high-altitude aircraft at low level or at high speed, but not at both, at least for any extended time. The new, low-level, high-speed tactics would only be practical for specialized, low-altitude bombers that had small-area, highly loaded wings, like the later TSR2 and Jaguar.
The F-104 just happened to fit this emerging requirement. While Lockheed designed the Starfighter for high-altitude, the requirement was for a high-G, supersonic dogfighter rather than a bomber interceptor. Supersonic turns would have subjected a conventional wing to enormous stresses and required an impractically strong and heavy structure. So Lockheed adopted a stiff, short-span, heavily loaded wing design that turned out to be almost ideal for high-speed, low-level flight. The USAF never actually needed the supersonic dogfighter, and few F-104As were built. But, once the rest of the structure was beefed up to match the inherent capabilities of the wing and the excellent J-79 engine, the F-104G was almost exactly what the Germans wanted.
In my opinion, Germany's requirements were short-sighted, narrow-minded, and overly theoretical. In hindsight, a single-purpose, short-range, low-level, nuclear-armed attack bomber was not the best choice. A general-purpose fighter-bomber would probably have been a better choice in the long run. But, on the other hand, it is hard to argue with success. The F-104G could be counted as a success simply because it never had to be used in its intended role.