On 1 September 1939, only minutes after the German Luftwaffe (Airforce) had begun the invasion of Poland by dropping bombs in a series of raids on the city of Wieluń by Junkers Ju 87 Stukas, at 04:48 local time, the battleship "Schleswig-Holstein", then on a "courtesy visit" to the Free City of Danzig, without warning opened fire on the Polish garrison. This was followed by an attack by "Oblt." Wilhelm Henningsen’s storm unit from the Schleswig-Holstein and the "Marinestosstruppkompanie". However, soon after crossing the artillery-breached brick wall, the attackers were ambushed by the Polish defenders, with small arms, mortar and machine-gun fire from concealed and well-positioned firing points that caught them in a crossfire. Another two assaults that day were repelled as well, with the Germans suffering unexpectedly high losses.