Not true at all. Runways were targeted as well as the hangers, fuel/ammo dumps, etc. One of the most effective ways of closing down an airfield is destroying its runways, even on unprepared grass/dirt airfields.
Are you implying that Germany did not have any "prepared" airfields and only operated from grass/dirt strips on unprepared airbases?
ack-ack
Did not mean that Germany had no prepared fields, its just that the Germans knew from the start, their fighters would be of greatest benefit in defending the home land and they figured, at least from books reflecting the German Air Force during WW2, that it was a lot easier to hide their fighters among trees, barns and etc. That is why the 109 and 190 series of aircraft had landing gear designed to operate off of unprepared fields. How many fighters did you see taking off from a prepared runway, in actual films made during the war? There were no military airfields build by the Germans, because of the WW1 treaty agreements, so they just used civilian air fields, until late 1942 and most were destroyed by allied bombing raids.
