The Germans used mines for aircraft and rocket production. They used mines to store their gold and art treasures. Why did they do this? Because the 8th Air Force did not have the capability to bomb underground mines with any result besides a little rubble at the entrance that could be cleared away in an hour or two.
They bombed oil refineries for months with thousands of bombers and many thousands of tons of bombs. The refineries were right out in the open. The refineries were severely damaged, but were still producing refined petroleum products on the day that the war ended.
Do not ask this question of any 8th Air Force veterans. They are getting old and the uncontrollable fits of laughter could be fatal.
What centurion316.
The pretext the British used to make the Italian campaign (some of the toughest fighting of the war) was to seize 13 airfields in southern Italy, as they lay within bomber range of the oil fields and refineries in Romania. After that objective was achieved, there was no further point to the Italian campaign. The British pushed for it, in order to avoid a cross-channel invasion into France. They failed.