Flak used in a ground attack role during an assault.
I read
"Flakartillerie greift an" a few days ago and it had this interesting statistics on the last page.
Destroyed by Flakartillery (everything from light 20mm AA to the 88) from 1. September 1939 to the 31. October 1941:
5381 Airplanes
1253 Bunkers
34 Armored Forts
1930 Tanks
279 Battery positions (artillery?)
2901 Cannons, Antitank guns, Mortars
5361 MG positions
5024 Trucks
119 columns (infantry?)
55 Transport trains
4 Destroyers
19 Warships
16 Transport ships
1 citadel
32 Ammunition depots
Even if the numbers might be too high (it´s from a 1941 propaganda book) the relation shows that the AA guns played a very important role in Poland, Fall gelb and the battle of france to enable the fast advances during that time.