Defense of Brest Fortress
The defense of Brest Fortress was the first battle of Operation Barbarossa, the Axis invasion of the Soviet Union launched on 22 June 1941. The German Army attacked without warning, expecting to take Brest on the first day, using only infantry and artillery, but it took them a week, and only after two bombardments by the Luftwaffe.
Source: Wikipedia — Defense of Brest Fortress (CC BY-SA 4.0)