In 1925 the Council of the League of Nations allowed Poland to keep 88 soldiers on Westerplatte. By September 1939 the crew of Westerplatte increased to 182 soldiers. They were armed with one 75 mm field gun, 2 anti-tank guns, 4 mortars and a number of machineguns. There were no real fortifications, only several concrete blockhouses in the forrest. The Polish garrison was separated from Gdansk city with the harbour channel, and a thin wall from the land only. In case of war, the defenders were supposed to withstand for 12 hours. The commander was Major Henryk Sucharski, the 2nd in comand was Captain Franciszek Dąbrowski (according to recent opinions, since 2 September Captain Dąbrowski was also the actual commander, after Sucharski's breakdown).
In the end of August 1939 the German old battleship Schleswig-Holstein came to Gdansk under the pretext of a courtesy visit, and anchored in the channel, near Westerplatte. On 1 September 1939, at 4.45 a.m., as the German Army started an invasion of Poland, Schleswig-Holstein started to shell Polish garrison with a heavy artillery barrage, including 280 mm and 150 mm guns. The following assault of the German naval infantry, hoping for an easy victory, was however repelled with Polish machinegun fire. Another two assaults of that day were repelled as well, and the Germans suffered quite a losses. The only Polish 75 mm gun was destroyed after shooting 28 shells at the German positions across the channel. On next days, the Germans bombarded Westerplatte with ship and field heavy artillery and with air raids of Junkers Ju 87 Stukas. Repeating attacks of German naval infantry, SS Heimwehr Danzig and combat engineers were all repelled by the Poles. Finally, Westerplatte crew surrendered on 7 September, being exhausted, lacking of food, water, ammunition and medicines.
The exact number of German losses is not known, estimated some 300-400 killed and many wounded. Surprisingly, the Polish casaulties were 15 killed and 53 wounded.